function deposit(address asset, uint256 amount, address onBehalfOf, uint16 referralCode)

function withdraw(address asset,uint256 amount,address to) external override whenNotPaused returns (uint256) 

function borrow(address asset,uint256 amount,uint256 interestRateMode,uint16 referralCode, address onBehalfOf)

function repay( address asset,uint256 amount,uint256 rateMode,address onBehalfOf) external override whenNotPaused returns (uint256)

function liquidationCall(address collateralAsset,address debtAsset,address user,uint256 debtToCover,bool receiveAToken)

function flashLoan(
    address receiverAddress,
    address[] calldata assets,
    uint256[] calldata amounts,
    uint256[] calldata modes,
    address onBehalfOf,
    bytes calldata params,
    uint16 referralCode
  )

    function calculateInterestRates(
        address _reserve,
        uint256 _availableLiquidity,
        uint256 _totalBorrowsStable,
        uint256 _totalBorrowsVariable,
        uint256 _averageStableBorrowRate
    )
        external
        view
        returns (
            uint256 currentLiquidityRate,
            uint256 currentStableBorrowRate,
            uint256 currentVariableBorrowRate
        )
    {
        uint256 totalBorrows = _totalBorrowsStable.add(_totalBorrowsVariable);

        uint256 utilizationRate = (totalBorrows == 0 && _availableLiquidity == 0)
            ? 0
            : totalBorrows.rayDiv(_availableLiquidity.add(totalBorrows));

        currentStableBorrowRate = ILendingRateOracle(addressesProvider.getLendingRateOracle())
            .getMarketBorrowRate(_reserve);

        if (utilizationRate > OPTIMAL_UTILIZATION_RATE) {
            uint256 excessUtilizationRateRatio = utilizationRate
                .sub(OPTIMAL_UTILIZATION_RATE)
                .rayDiv(EXCESS_UTILIZATION_RATE);

            currentStableBorrowRate = currentStableBorrowRate.add(stableRateSlope1).add(
                stableRateSlope2.rayMul(excessUtilizationRateRatio)
            );

            currentVariableBorrowRate = baseVariableBorrowRate.add(variableRateSlope1).add(
                variableRateSlope2.rayMul(excessUtilizationRateRatio)
            );
        } else {
            currentStableBorrowRate = currentStableBorrowRate.add(
                stableRateSlope1.rayMul(
                    utilizationRate.rayDiv(
                        OPTIMAL_UTILIZATION_RATE
                    )
                )
            );
            currentVariableBorrowRate = baseVariableBorrowRate.add(
                utilizationRate.rayDiv(OPTIMAL_UTILIZATION_RATE).rayMul(variableRateSlope1)
            );
        }

        currentLiquidityRate = getOverallBorrowRateInternal(
            _totalBorrowsStable,
            _totalBorrowsVariable,
            currentVariableBorrowRate,
            _averageStableBorrowRate
        )
            .rayMul(utilizationRate);

    }

    function getOverallBorrowRateInternal(
        uint256 _totalBorrowsStable,
        uint256 _totalBorrowsVariable,
        uint256 _currentVariableBorrowRate,
        uint256 _currentAverageStableBorrowRate
    ) internal pure returns (uint256) {
        uint256 totalBorrows = _totalBorrowsStable.add(_totalBorrowsVariable);

        if (totalBorrows == 0) return 0;

        uint256 weightedVariableRate = _totalBorrowsVariable.wadToRay().rayMul(
            _currentVariableBorrowRate
        );

        uint256 weightedStableRate = _totalBorrowsStable.wadToRay().rayMul(
            _currentAverageStableBorrowRate
        );

        uint256 overallBorrowRate = weightedVariableRate.add(weightedStableRate).rayDiv(
            totalBorrows.wadToRay()
        );

        return overallBorrowRate;
    }

    /**
    * @dev deposits The underlying asset into the reserve. A corresponding amount of the overlying asset (aTokens)
    * is minted.
    * @param _reserve the address of the reserve
    * @param _amount the amount to be deposited
    * @param _referralCode integrators are assigned a referral code and can potentially receive rewards.
    **/
    function deposit(address _reserve, uint256 _amount, uint16 _referralCode)
        external
        payable
        nonReentrant
        onlyActiveReserve(_reserve)
        onlyUnfreezedReserve(_reserve)
        onlyAmountGreaterThanZero(_amount)
    {
        AToken aToken = AToken(core.getReserveATokenAddress(_reserve));

        bool isFirstDeposit = aToken.balanceOf(msg.sender) == 0;

        core.updateStateOnDeposit(_reserve, msg.sender, _amount, isFirstDeposit);

        //minting AToken to user 1:1 with the specific exchange rate
        aToken.mintOnDeposit(msg.sender, _amount);

        //transfer to the core contract
        core.transferToReserve.value(msg.value)(_reserve, msg.sender, _amount);

        //solium-disable-next-line
        emit Deposit(_reserve, msg.sender, _amount, _referralCode, block.timestamp);

    }

    /**
    * @dev Redeems the underlying amount of assets requested by _user.
    * This function is executed by the overlying aToken contract in response to a redeem action.
    * @param _reserve the address of the reserve
    * @param _user the address of the user performing the action
    * @param _amount the underlying amount to be redeemed
    **/
    function redeemUnderlying(
        address _reserve,
        address payable _user,
        uint256 _amount,
        uint256 _aTokenBalanceAfterRedeem
    )
        external
        nonReentrant
        onlyOverlyingAToken(_reserve)
        onlyActiveReserve(_reserve)
        onlyAmountGreaterThanZero(_amount)
    {
        uint256 currentAvailableLiquidity = core.getReserveAvailableLiquidity(_reserve);
        require(
            currentAvailableLiquidity >= _amount,
            "There is not enough liquidity available to redeem"
        );

        core.updateStateOnRedeem(_reserve, _user, _amount, _aTokenBalanceAfterRedeem == 0);

        core.transferToUser(_reserve, _user, _amount);

        //solium-disable-next-line
        emit RedeemUnderlying(_reserve, _user, _amount, block.timestamp);

    }

    /**
    * @dev data structures for local computations in the borrow() method.
    */

    struct BorrowLocalVars {
        uint256 principalBorrowBalance;
        uint256 currentLtv;
        uint256 currentLiquidationThreshold;
        uint256 borrowFee;
        uint256 requestedBorrowAmountETH;
        uint256 amountOfCollateralNeededETH;
        uint256 userCollateralBalanceETH;
        uint256 userBorrowBalanceETH;
        uint256 userTotalFeesETH;
        uint256 borrowBalanceIncrease;
        uint256 currentReserveStableRate;
        uint256 availableLiquidity;
        uint256 reserveDecimals;
        uint256 finalUserBorrowRate;
        CoreLibrary.InterestRateMode rateMode;
        bool healthFactorBelowThreshold;
    }

    /**
    * @dev Allows users to borrow a specific amount of the reserve currency, provided that the borrower
    * already deposited enough collateral.
    * @param _reserve the address of the reserve
    * @param _amount the amount to be borrowed
    * @param _interestRateMode the interest rate mode at which the user wants to borrow. Can be 0 (STABLE) or 1 (VARIABLE)
    **/
    function borrow(
        address _reserve,
        uint256 _amount,
        uint256 _interestRateMode,
        uint16 _referralCode
    )
        external
        nonReentrant
        onlyActiveReserve(_reserve)
        onlyUnfreezedReserve(_reserve)
        onlyAmountGreaterThanZero(_amount)
    {
        // Usage of a memory struct of vars to avoid "Stack too deep" errors due to local variables
        BorrowLocalVars memory vars;

        //check that the reserve is enabled for borrowing
        require(core.isReserveBorrowingEnabled(_reserve), "Reserve is not enabled for borrowing");
        //validate interest rate mode
        require(
            uint256(CoreLibrary.InterestRateMode.VARIABLE) == _interestRateMode ||
                uint256(CoreLibrary.InterestRateMode.STABLE) == _interestRateMode,
            "Invalid interest rate mode selected"
        );

        //cast the rateMode to coreLibrary.interestRateMode
        vars.rateMode = CoreLibrary.InterestRateMode(_interestRateMode);

        //check that the amount is available in the reserve
        vars.availableLiquidity = core.getReserveAvailableLiquidity(_reserve);

        require(
            vars.availableLiquidity >= _amount,
            "There is not enough liquidity available in the reserve"
        );

        (
            ,
            vars.userCollateralBalanceETH,
            vars.userBorrowBalanceETH,
            vars.userTotalFeesETH,
            vars.currentLtv,
            vars.currentLiquidationThreshold,
            ,
            vars.healthFactorBelowThreshold
        ) = dataProvider.calculateUserGlobalData(msg.sender);

        require(vars.userCollateralBalanceETH > 0, "The collateral balance is 0");

        require(
            !vars.healthFactorBelowThreshold,
            "The borrower can already be liquidated so he cannot borrow more"
        );

        //calculating fees
        vars.borrowFee = feeProvider.calculateLoanOriginationFee(msg.sender, _amount);

        require(vars.borrowFee > 0, "The amount to borrow is too small");

        vars.amountOfCollateralNeededETH = dataProvider.calculateCollateralNeededInETH(
            _reserve,
            _amount,
            vars.borrowFee,
            vars.userBorrowBalanceETH,
            vars.userTotalFeesETH,
            vars.currentLtv
        );

        require(
            vars.amountOfCollateralNeededETH <= vars.userCollateralBalanceETH,
            "There is not enough collateral to cover a new borrow"
        );

        /**
        * Following conditions need to be met if the user is borrowing at a stable rate:
        * 1. Reserve must be enabled for stable rate borrowing
        * 2. Users cannot borrow from the reserve if their collateral is (mostly) the same currency
        *    they are borrowing, to prevent abuses.
        * 3. Users will be able to borrow only a relatively small, configurable amount of the total
        *    liquidity
        **/

        if (vars.rateMode == CoreLibrary.InterestRateMode.STABLE) {
            //check if the borrow mode is stable and if stable rate borrowing is enabled on this reserve
            require(
                core.isUserAllowedToBorrowAtStable(_reserve, msg.sender, _amount),
                "User cannot borrow the selected amount with a stable rate"
            );

            //calculate the max available loan size in stable rate mode as a percentage of the
            //available liquidity
            uint256 maxLoanPercent = parametersProvider.getMaxStableRateBorrowSizePercent();
            uint256 maxLoanSizeStable = vars.availableLiquidity.mul(maxLoanPercent).div(100);

            require(
                _amount <= maxLoanSizeStable,
                "User is trying to borrow too much liquidity at a stable rate"
            );
        }

        //all conditions passed - borrow is accepted
        (vars.finalUserBorrowRate, vars.borrowBalanceIncrease) = core.updateStateOnBorrow(
            _reserve,
            msg.sender,
            _amount,
            vars.borrowFee,
            vars.rateMode
        );

        //if we reached this point, we can transfer
        core.transferToUser(_reserve, msg.sender, _amount);

        emit Borrow(
            _reserve,
            msg.sender,
            _amount,
            _interestRateMode,
            vars.finalUserBorrowRate,
            vars.borrowFee,
            vars.borrowBalanceIncrease,
            _referralCode,
            //solium-disable-next-line
            block.timestamp
        );
    }

    /**
    * @notice repays a borrow on the specific reserve, for the specified amount (or for the whole amount, if uint256(-1) is specified).
    * @dev the target user is defined by _onBehalfOf. If there is no repayment on behalf of another account,
    * _onBehalfOf must be equal to msg.sender.
    * @param _reserve the address of the reserve on which the user borrowed
    * @param _amount the amount to repay, or uint256(-1) if the user wants to repay everything
    * @param _onBehalfOf the address for which msg.sender is repaying.
    **/

    struct RepayLocalVars {
        uint256 principalBorrowBalance;
        uint256 compoundedBorrowBalance;
        uint256 borrowBalanceIncrease;
        bool isETH;
        uint256 paybackAmount;
        uint256 paybackAmountMinusFees;
        uint256 currentStableRate;
        uint256 originationFee;
    }

    function repay(address _reserve, uint256 _amount, address payable _onBehalfOf)
        external
        payable
        nonReentrant
        onlyActiveReserve(_reserve)
        onlyAmountGreaterThanZero(_amount)
    {
        // Usage of a memory struct of vars to avoid "Stack too deep" errors due to local variables
        RepayLocalVars memory vars;

        (
            vars.principalBorrowBalance,
            vars.compoundedBorrowBalance,
            vars.borrowBalanceIncrease
        ) = core.getUserBorrowBalances(_reserve, _onBehalfOf);

        vars.originationFee = core.getUserOriginationFee(_reserve, _onBehalfOf);
        vars.isETH = EthAddressLib.ethAddress() == _reserve;

        require(vars.compoundedBorrowBalance > 0, "The user does not have any borrow pending");

        require(
            _amount != UINT_MAX_VALUE || msg.sender == _onBehalfOf,
            "To repay on behalf of an user an explicit amount to repay is needed."
        );

        //default to max amount
        vars.paybackAmount = vars.compoundedBorrowBalance.add(vars.originationFee);

        if (_amount != UINT_MAX_VALUE && _amount < vars.paybackAmount) {
            vars.paybackAmount = _amount;
        }

        require(
            !vars.isETH || msg.value >= vars.paybackAmount,
            "Invalid msg.value sent for the repayment"
        );

        //if the amount is smaller than the origination fee, just transfer the amount to the fee destination address
        if (vars.paybackAmount <= vars.originationFee) {
            core.updateStateOnRepay(
                _reserve,
                _onBehalfOf,
                0,
                vars.paybackAmount,
                vars.borrowBalanceIncrease,
                false
            );

            core.transferToFeeCollectionAddress.value(vars.isETH ? vars.paybackAmount : 0)(
                _reserve,
                _onBehalfOf,
                vars.paybackAmount,
                addressesProvider.getTokenDistributor()
            );

            emit Repay(
                _reserve,
                _onBehalfOf,
                msg.sender,
                0,
                vars.paybackAmount,
                vars.borrowBalanceIncrease,
                //solium-disable-next-line
                block.timestamp
            );
            return;
        }

        vars.paybackAmountMinusFees = vars.paybackAmount.sub(vars.originationFee);

        core.updateStateOnRepay(
            _reserve,
            _onBehalfOf,
            vars.paybackAmountMinusFees,
            vars.originationFee,
            vars.borrowBalanceIncrease,
            vars.compoundedBorrowBalance == vars.paybackAmountMinusFees
        );

        //if the user didn't repay the origination fee, transfer the fee to the fee collection address
        if(vars.originationFee > 0) {
            core.transferToFeeCollectionAddress.value(vars.isETH ? vars.originationFee : 0)(
                _reserve,
                msg.sender,
                vars.originationFee,
                addressesProvider.getTokenDistributor()
            );
        }

        //sending the total msg.value if the transfer is ETH.
        //the transferToReserve() function will take care of sending the
        //excess ETH back to the caller
        core.transferToReserve.value(vars.isETH ? msg.value.sub(vars.originationFee) : 0)(
            _reserve,
            msg.sender,
            vars.paybackAmountMinusFees
        );

        emit Repay(
            _reserve,
            _onBehalfOf,
            msg.sender,
            vars.paybackAmountMinusFees,
            vars.originationFee,
            vars.borrowBalanceIncrease,
            //solium-disable-next-line
            block.timestamp
        );
    }

    /**
    * @dev borrowers can user this function to swap between stable and variable borrow rate modes.
    * @param _reserve the address of the reserve on which the user borrowed
    **/
    function swapBorrowRateMode(address _reserve)
        external
        nonReentrant
        onlyActiveReserve(_reserve)
        onlyUnfreezedReserve(_reserve)
    {
        (uint256 principalBorrowBalance, uint256 compoundedBorrowBalance, uint256 borrowBalanceIncrease) = core
            .getUserBorrowBalances(_reserve, msg.sender);

        require(
            compoundedBorrowBalance > 0,
            "User does not have a borrow in progress on this reserve"
        );

        CoreLibrary.InterestRateMode currentRateMode = core.getUserCurrentBorrowRateMode(
            _reserve,
            msg.sender
        );

        if (currentRateMode == CoreLibrary.InterestRateMode.VARIABLE) {
            /**
            * user wants to swap to stable, before swapping we need to ensure that
            * 1. stable borrow rate is enabled on the reserve
            * 2. user is not trying to abuse the reserve by depositing
            * more collateral than he is borrowing, artificially lowering
            * the interest rate, borrowing at variable, and switching to stable
            **/
            require(
                core.isUserAllowedToBorrowAtStable(_reserve, msg.sender, compoundedBorrowBalance),
                "User cannot borrow the selected amount at stable"
            );
        }

        (CoreLibrary.InterestRateMode newRateMode, uint256 newBorrowRate) = core
            .updateStateOnSwapRate(
            _reserve,
            msg.sender,
            principalBorrowBalance,
            compoundedBorrowBalance,
            borrowBalanceIncrease,
            currentRateMode
        );

        emit Swap(
            _reserve,
            msg.sender,
            uint256(newRateMode),
            newBorrowRate,
            borrowBalanceIncrease,
            //solium-disable-next-line
            block.timestamp
        );
    }

    /**
    * @dev rebalances the stable interest rate of a user if current liquidity rate > user stable rate.
    * this is regulated by Aave to ensure that the protocol is not abused, and the user is paying a fair
    * rate. Anyone can call this function though.
    * @param _reserve the address of the reserve
    * @param _user the address of the user to be rebalanced
    **/
    function rebalanceStableBorrowRate(address _reserve, address _user)
        external
        nonReentrant
        onlyActiveReserve(_reserve)
    {
        (, uint256 compoundedBalance, uint256 borrowBalanceIncrease) = core.getUserBorrowBalances(
            _reserve,
            _user
        );

        //step 1: user must be borrowing on _reserve at a stable rate
        require(compoundedBalance > 0, "User does not have any borrow for this reserve");

        require(
            core.getUserCurrentBorrowRateMode(_reserve, _user) ==
                CoreLibrary.InterestRateMode.STABLE,
            "The user borrow is variable and cannot be rebalanced"
        );

        uint256 userCurrentStableRate = core.getUserCurrentStableBorrowRate(_reserve, _user);
        uint256 liquidityRate = core.getReserveCurrentLiquidityRate(_reserve);
        uint256 reserveCurrentStableRate = core.getReserveCurrentStableBorrowRate(_reserve);
        uint256 rebalanceDownRateThreshold = reserveCurrentStableRate.rayMul(
            WadRayMath.ray().add(parametersProvider.getRebalanceDownRateDelta())
        );

        //step 2: we have two possible situations to rebalance:

        //1. user stable borrow rate is below the current liquidity rate. The loan needs to be rebalanced,
        //as this situation can be abused (user putting back the borrowed liquidity in the same reserve to earn on it)
        //2. user stable rate is above the market avg borrow rate of a certain delta, and utilization rate is low.
        //In this case, the user is paying an interest that is too high, and needs to be rescaled down.
        if (
            userCurrentStableRate < liquidityRate ||
            userCurrentStableRate > rebalanceDownRateThreshold
        ) {
            uint256 newStableRate = core.updateStateOnRebalance(
                _reserve,
                _user,
                borrowBalanceIncrease
            );

            emit RebalanceStableBorrowRate(
                _reserve,
                _user,
                newStableRate,
                borrowBalanceIncrease,
                //solium-disable-next-line
                block.timestamp
            );

            return;

        }

        revert("Interest rate rebalance conditions were not met");
    }

    /**
    * @dev allows depositors to enable or disable a specific deposit as collateral.
    * @param _reserve the address of the reserve
    * @param _useAsCollateral true if the user wants to user the deposit as collateral, false otherwise.
    **/
    function setUserUseReserveAsCollateral(address _reserve, bool _useAsCollateral)
        external
        nonReentrant
        onlyActiveReserve(_reserve)
        onlyUnfreezedReserve(_reserve)
    {
        uint256 underlyingBalance = core.getUserUnderlyingAssetBalance(_reserve, msg.sender);

        require(underlyingBalance > 0, "User does not have any liquidity deposited");

        require(
            dataProvider.balanceDecreaseAllowed(_reserve, msg.sender, underlyingBalance),
            "User deposit is already being used as collateral"
        );

        core.setUserUseReserveAsCollateral(_reserve, msg.sender, _useAsCollateral);

        if (_useAsCollateral) {
            emit ReserveUsedAsCollateralEnabled(_reserve, msg.sender);
        } else {
            emit ReserveUsedAsCollateralDisabled(_reserve, msg.sender);
        }
    }

    /**
    * @dev users can invoke this function to liquidate an undercollateralized position.
    * @param _reserve the address of the collateral to liquidated
    * @param _reserve the address of the principal reserve
    * @param _user the address of the borrower
    * @param _purchaseAmount the amount of principal that the liquidator wants to repay
    * @param _receiveAToken true if the liquidators wants to receive the aTokens, false if
    * he wants to receive the underlying asset directly
    **/
    function liquidationCall(
        address _collateral,
        address _reserve,
        address _user,
        uint256 _purchaseAmount,
        bool _receiveAToken
    ) external payable nonReentrant onlyActiveReserve(_reserve) onlyActiveReserve(_collateral) {
        address liquidationManager = addressesProvider.getLendingPoolLiquidationManager();

        //solium-disable-next-line
        (bool success, bytes memory result) = liquidationManager.delegatecall(
            abi.encodeWithSignature(
                "liquidationCall(address,address,address,uint256,bool)",
                _collateral,
                _reserve,
                _user,
                _purchaseAmount,
                _receiveAToken
            )
        );
        require(success, "Liquidation call failed");

        (uint256 returnCode, string memory returnMessage) = abi.decode(result, (uint256, string));

        if (returnCode != 0) {
            //error found
            revert(string(abi.encodePacked("Liquidation failed: ", returnMessage)));
        }
    }

    /**
    * @dev allows smartcontracts to access the liquidity of the pool within one transaction,
    * as long as the amount taken plus a fee is returned. NOTE There are security concerns for developers of flashloan receiver contracts
    * that must be kept into consideration. For further details please visit https://developers.aave.com
    * @param _receiver The address of the contract receiving the funds. The receiver should implement the IFlashLoanReceiver interface.
    * @param _reserve the address of the principal reserve
    * @param _amount the amount requested for this flashloan
    **/
    function flashLoan(address _receiver, address _reserve, uint256 _amount, bytes memory _params)
        public
        nonReentrant
        onlyActiveReserve(_reserve)
        onlyAmountGreaterThanZero(_amount)
    {
        //check that the reserve has enough available liquidity
        //we avoid using the getAvailableLiquidity() function in LendingPoolCore to save gas
        uint256 availableLiquidityBefore = _reserve == EthAddressLib.ethAddress()
            ? address(core).balance
            : IERC20(_reserve).balanceOf(address(core));

        require(
            availableLiquidityBefore >= _amount,
            "There is not enough liquidity available to borrow"
        );

        (uint256 totalFeeBips, uint256 protocolFeeBips) = parametersProvider
            .getFlashLoanFeesInBips();
        //calculate amount fee
        uint256 amountFee = _amount.mul(totalFeeBips).div(10000);

        //protocol fee is the part of the amountFee reserved for the protocol - the rest goes to depositors
        uint256 protocolFee = amountFee.mul(protocolFeeBips).div(10000);
        require(
            amountFee > 0 && protocolFee > 0,
            "The requested amount is too small for a flashLoan."
        );

        //get the FlashLoanReceiver instance
        IFlashLoanReceiver receiver = IFlashLoanReceiver(_receiver);

        address payable userPayable = address(uint160(_receiver));

        //transfer funds to the receiver
        core.transferToUser(_reserve, userPayable, _amount);

        //execute action of the receiver
        receiver.executeOperation(_reserve, _amount, amountFee, _params);

        //check that the actual balance of the core contract includes the returned amount
        uint256 availableLiquidityAfter = _reserve == EthAddressLib.ethAddress()
            ? address(core).balance
            : IERC20(_reserve).balanceOf(address(core));

        require(
            availableLiquidityAfter == availableLiquidityBefore.add(amountFee),
            "The actual balance of the protocol is inconsistent"
        );

        core.updateStateOnFlashLoan(
            _reserve,
            availableLiquidityBefore,
            amountFee.sub(protocolFee),
            protocolFee
        );

        //solium-disable-next-line
        emit FlashLoan(_receiver, _reserve, _amount, amountFee, protocolFee, block.timestamp);
    }

    /**
    * @dev initializes a reserve
    * @param _reserve the address of the reserve to be initialized
    * @param _underlyingAssetDecimals the decimals of the reserve underlying asset
    * @param _interestRateStrategyAddress the address of the interest rate strategy contract for this reserve
    **/
    function initReserve(
        address _reserve,
        uint8 _underlyingAssetDecimals,
        address _interestRateStrategyAddress
    ) external onlyLendingPoolManager {
        ERC20Detailed asset = ERC20Detailed(_reserve);

        string memory aTokenName = string(abi.encodePacked("Aave Interest bearing ", asset.name()));
        string memory aTokenSymbol = string(abi.encodePacked("a", asset.symbol()));

        initReserveWithData(
            _reserve,
            aTokenName,
            aTokenSymbol,
            _underlyingAssetDecimals,
            _interestRateStrategyAddress
        );
    }

    /**
    * @dev initializes a reserve using aTokenData provided externally (useful if the underlying ERC20 contract doesn't expose name or decimals)
    * @param _reserve the address of the reserve to be initialized
    * @param _aTokenName the name of the aToken contract
    * @param _aTokenSymbol the symbol of the aToken contract
    * @param _underlyingAssetDecimals the decimals of the reserve underlying asset
    * @param _interestRateStrategyAddress the address of the interest rate strategy contract for this reserve
    **/
    function initReserveWithData(
        address _reserve,
        string memory _aTokenName,
        string memory _aTokenSymbol,
        uint8 _underlyingAssetDecimals,
        address _interestRateStrategyAddress
    ) public onlyLendingPoolManager {
        LendingPoolCore core = LendingPoolCore(poolAddressesProvider.getLendingPoolCore());

        AToken aTokenInstance = new AToken(
            poolAddressesProvider,
            _reserve,
            _underlyingAssetDecimals,
            _aTokenName,
            _aTokenSymbol
        );
        core.initReserve(
            _reserve,
            address(aTokenInstance),
            _underlyingAssetDecimals,
            _interestRateStrategyAddress
        );

        emit ReserveInitialized(
            _reserve,
            address(aTokenInstance),
            _interestRateStrategyAddress
        );
    }

		mapping(address => CoreLibrary.ReserveData) internal reserves;
    mapping(address => mapping(address => CoreLibrary.UserReserveData)) internal usersReserveData;

    address[] public reservesList;

    uint256 public constant CORE_REVISION = 0x6;

    function updateReserveInterestRatesAndTimestampInternal(
        address _reserve,
        uint256 _liquidityAdded,
        uint256 _liquidityTaken
    ) internal {
        CoreLibrary.ReserveData storage reserve = reserves[_reserve];
        (uint256 newLiquidityRate, uint256 newStableRate, uint256 newVariableRate) = IReserveInterestRateStrategy(
            reserve
                .interestRateStrategyAddress
        )
            .calculateInterestRates(
            _reserve,
            getReserveAvailableLiquidity(_reserve).add(_liquidityAdded).sub(_liquidityTaken),
            reserve.totalBorrowsStable,
            reserve.totalBorrowsVariable,
            reserve.currentAverageStableBorrowRate
        );

        reserve.currentLiquidityRate = newLiquidityRate;
        reserve.currentStableBorrowRate = newStableRate;
        reserve.currentVariableBorrowRate = newVariableRate;

        //solium-disable-next-line
        reserve.lastUpdateTimestamp = uint40(block.timestamp);

        emit ReserveUpdated(
            _reserve,
            newLiquidityRate,
            newStableRate,
            newVariableRate,
            reserve.lastLiquidityCumulativeIndex,
            reserve.lastVariableBorrowCumulativeIndex
        );
    }

    function transferFlashLoanProtocolFeeInternal(address _token, uint256 _amount) internal {
        address payable receiver = address(uint160(addressesProvider.getTokenDistributor()));

        if (_token != EthAddressLib.ethAddress()) {
            ERC20(_token).safeTransfer(receiver, _amount);
        } else {
            //solium-disable-next-line
            (bool result, ) = receiver.call.value(_amount)("");
            require(result, "Transfer to token distributor failed");
        }
    }

    /**
    * @dev initializes the Core contract, invoked upon registration on the AddressesProvider
    * @param _addressesProvider the addressesProvider contract
    **/

    function initialize(LendingPoolAddressesProvider _addressesProvider) public initializer {
        addressesProvider = _addressesProvider;
        refreshConfigInternal();
    }
    /**
    * @dev updates the internal configuration of the core
    **/
    function refreshConfigInternal() internal {
        lendingPoolAddress = addressesProvider.getLendingPool();
    }

    /**
    * @dev updates the state of the core as a result of a deposit action
    * @param _reserve the address of the reserve in which the deposit is happening
    * @param _user the address of the the user depositing
    * @param _amount the amount being deposited
    * @param _isFirstDeposit true if the user is depositing for the first time
    **/

    function updateStateOnDeposit(
        address _reserve,
        address _user,
        uint256 _amount,
        bool _isFirstDeposit
    ) external onlyLendingPool {
        reserves[_reserve].updateCumulativeIndexes();
        updateReserveInterestRatesAndTimestampInternal(_reserve, _amount, 0);

        if (_isFirstDeposit) {
            //if this is the first deposit of the user, we configure the deposit as enabled to be used as collateral
            setUserUseReserveAsCollateral(_reserve, _user, true);
        }
    }

    /**
    * @dev updates the state of the core as a result of a redeem action
    * @param _reserve the address of the reserve in which the redeem is happening
    * @param _user the address of the the user redeeming
    * @param _amountRedeemed the amount being redeemed
    * @param _userRedeemedEverything true if the user is redeeming everything
    **/
    function updateStateOnRedeem(
        address _reserve,
        address _user,
        uint256 _amountRedeemed,
        bool _userRedeemedEverything
    ) external onlyLendingPool {
        //compound liquidity and variable borrow interests
        reserves[_reserve].updateCumulativeIndexes();
        updateReserveInterestRatesAndTimestampInternal(_reserve, 0, _amountRedeemed);

        //if user redeemed everything the useReserveAsCollateral flag is reset
        if (_userRedeemedEverything) {
            setUserUseReserveAsCollateral(_reserve, _user, false);
        }
    }

    /**
    * @dev updates the state of the core as a result of a flashloan action
    * @param _reserve the address of the reserve in which the flashloan is happening
    * @param _income the income of the protocol as a result of the action
    **/
    function updateStateOnFlashLoan(
        address _reserve,
        uint256 _availableLiquidityBefore,
        uint256 _income,
        uint256 _protocolFee
    ) external onlyLendingPool {
        transferFlashLoanProtocolFeeInternal(_reserve, _protocolFee);

        //compounding the cumulated interest
        reserves[_reserve].updateCumulativeIndexes();

        uint256 totalLiquidityBefore = _availableLiquidityBefore.add(
            getReserveTotalBorrows(_reserve)
        );

        //compounding the received fee into the reserve
        reserves[_reserve].cumulateToLiquidityIndex(totalLiquidityBefore, _income);

        //refresh interest rates
        updateReserveInterestRatesAndTimestampInternal(_reserve, _income, 0);
    }

    /**
    * @dev updates the state of the core as a consequence of a borrow action.
    * @param _reserve the address of the reserve on which the user is borrowing
    * @param _user the address of the borrower
    * @param _amountBorrowed the new amount borrowed
    * @param _borrowFee the fee on the amount borrowed
    * @param _rateMode the borrow rate mode (stable, variable)
    * @return the new borrow rate for the user
    **/
    function updateStateOnBorrow(
        address _reserve,
        address _user,
        uint256 _amountBorrowed,
        uint256 _borrowFee,
        CoreLibrary.InterestRateMode _rateMode
    ) external onlyLendingPool returns (uint256, uint256) {
        // getting the previous borrow data of the user
        (uint256 principalBorrowBalance, , uint256 balanceIncrease) = getUserBorrowBalances(
            _reserve,
            _user
        );

        updateReserveStateOnBorrowInternal(
            _reserve,
            _user,
            principalBorrowBalance,
            balanceIncrease,
            _amountBorrowed,
            _rateMode
        );

        updateUserStateOnBorrowInternal(
            _reserve,
            _user,
            _amountBorrowed,
            balanceIncrease,
            _borrowFee,
            _rateMode
        );

        updateReserveInterestRatesAndTimestampInternal(_reserve, 0, _amountBorrowed);

        return (getUserCurrentBorrowRate(_reserve, _user), balanceIncrease);
    }

    /**
    * @dev updates the state of the core as a consequence of a repay action.
    * @param _reserve the address of the reserve on which the user is repaying
    * @param _user the address of the borrower
    * @param _paybackAmountMinusFees the amount being paid back minus fees
    * @param _originationFeeRepaid the fee on the amount that is being repaid
    * @param _balanceIncrease the accrued interest on the borrowed amount
    * @param _repaidWholeLoan true if the user is repaying the whole loan
    **/

    function updateStateOnRepay(
        address _reserve,
        address _user,
        uint256 _paybackAmountMinusFees,
        uint256 _originationFeeRepaid,
        uint256 _balanceIncrease,
        bool _repaidWholeLoan
    ) external onlyLendingPool {
        updateReserveStateOnRepayInternal(
            _reserve,
            _user,
            _paybackAmountMinusFees,
            _balanceIncrease
        );
        updateUserStateOnRepayInternal(
            _reserve,
            _user,
            _paybackAmountMinusFees,
            _originationFeeRepaid,
            _balanceIncrease,
            _repaidWholeLoan
        );

        updateReserveInterestRatesAndTimestampInternal(_reserve, _paybackAmountMinusFees, 0);
    }

    /**
    * @dev updates the state of the reserve as a consequence of a repay action.
    * @param _reserve the address of the reserve on which the user is repaying
    * @param _user the address of the borrower
    * @param _paybackAmountMinusFees the amount being paid back minus fees
    * @param _balanceIncrease the accrued interest on the borrowed amount
    **/

    function updateReserveStateOnRepayInternal(
        address _reserve,
        address _user,
        uint256 _paybackAmountMinusFees,
        uint256 _balanceIncrease
    ) internal {
        CoreLibrary.ReserveData storage reserve = reserves[_reserve];
        CoreLibrary.UserReserveData storage user = usersReserveData[_user][_reserve];

        CoreLibrary.InterestRateMode borrowRateMode = getUserCurrentBorrowRateMode(_reserve, _user);

        //update the indexes
        reserves[_reserve].updateCumulativeIndexes();

        //compound the cumulated interest to the borrow balance and then subtracting the payback amount
        if (borrowRateMode == CoreLibrary.InterestRateMode.STABLE) {
            reserve.increaseTotalBorrowsStableAndUpdateAverageRate(
                _balanceIncrease,
                user.stableBorrowRate
            );
            reserve.decreaseTotalBorrowsStableAndUpdateAverageRate(
                _paybackAmountMinusFees,
                user.stableBorrowRate
            );
        } else {
            reserve.increaseTotalBorrowsVariable(_balanceIncrease);
            reserve.decreaseTotalBorrowsVariable(_paybackAmountMinusFees);
        }
    }

    /**
    * @dev updates the state of the user as a consequence of a repay action.
    * @param _reserve the address of the reserve on which the user is repaying
    * @param _user the address of the borrower
    * @param _paybackAmountMinusFees the amount being paid back minus fees
    * @param _originationFeeRepaid the fee on the amount that is being repaid
    * @param _balanceIncrease the accrued interest on the borrowed amount
    * @param _repaidWholeLoan true if the user is repaying the whole loan
    **/
    function updateUserStateOnRepayInternal(
        address _reserve,
        address _user,
        uint256 _paybackAmountMinusFees,
        uint256 _originationFeeRepaid,
        uint256 _balanceIncrease,
        bool _repaidWholeLoan
    ) internal {
        CoreLibrary.ReserveData storage reserve = reserves[_reserve];
        CoreLibrary.UserReserveData storage user = usersReserveData[_user][_reserve];

        //update the user principal borrow balance, adding the cumulated interest and then subtracting the payback amount
        user.principalBorrowBalance = user.principalBorrowBalance.add(_balanceIncrease).sub(
            _paybackAmountMinusFees
        );
        user.lastVariableBorrowCumulativeIndex = reserve.lastVariableBorrowCumulativeIndex;

        //if the balance decrease is equal to the previous principal (user is repaying the whole loan)
        //and the rate mode is stable, we reset the interest rate mode of the user
        if (_repaidWholeLoan) {
            user.stableBorrowRate = 0;
            user.lastVariableBorrowCumulativeIndex = 0;
        }
        user.originationFee = user.originationFee.sub(_originationFeeRepaid);

        //solium-disable-next-line
        user.lastUpdateTimestamp = uint40(block.timestamp);

    }

    /**
    * @dev updates the state of the core as a consequence of a swap rate action.
    * @param _reserve the address of the reserve on which the user is repaying
    * @param _user the address of the borrower
    * @param _principalBorrowBalance the amount borrowed by the user
    * @param _compoundedBorrowBalance the amount borrowed plus accrued interest
    * @param _balanceIncrease the accrued interest on the borrowed amount
    * @param _currentRateMode the current interest rate mode for the user
    **/
    function updateStateOnSwapRate(
        address _reserve,
        address _user,
        uint256 _principalBorrowBalance,
        uint256 _compoundedBorrowBalance,
        uint256 _balanceIncrease,
        CoreLibrary.InterestRateMode _currentRateMode
    ) external onlyLendingPool returns (CoreLibrary.InterestRateMode, uint256) {
        updateReserveStateOnSwapRateInternal(
            _reserve,
            _user,
            _principalBorrowBalance,
            _compoundedBorrowBalance,
            _currentRateMode
        );

        CoreLibrary.InterestRateMode newRateMode = updateUserStateOnSwapRateInternal(
            _reserve,
            _user,
            _balanceIncrease,
            _currentRateMode
        );

        updateReserveInterestRatesAndTimestampInternal(_reserve, 0, 0);

        return (newRateMode, getUserCurrentBorrowRate(_reserve, _user));
    }

    /**
    * @dev updates the state of the user as a consequence of a swap rate action.
    * @param _reserve the address of the reserve on which the user is performing the rate swap
    * @param _user the address of the borrower
    * @param _principalBorrowBalance the the principal amount borrowed by the user
    * @param _compoundedBorrowBalance the principal amount plus the accrued interest
    * @param _currentRateMode the rate mode at which the user borrowed
    **/
    function updateReserveStateOnSwapRateInternal(
        address _reserve,
        address _user,
        uint256 _principalBorrowBalance,
        uint256 _compoundedBorrowBalance,
        CoreLibrary.InterestRateMode _currentRateMode
    ) internal {
        CoreLibrary.ReserveData storage reserve = reserves[_reserve];
        CoreLibrary.UserReserveData storage user = usersReserveData[_user][_reserve];

        //compounding reserve indexes
        reserve.updateCumulativeIndexes();

        if (_currentRateMode == CoreLibrary.InterestRateMode.STABLE) {
            uint256 userCurrentStableRate = user.stableBorrowRate;

            //swap to variable
            reserve.decreaseTotalBorrowsStableAndUpdateAverageRate(
                _principalBorrowBalance,
                userCurrentStableRate
            ); //decreasing stable from old principal balance
            reserve.increaseTotalBorrowsVariable(_compoundedBorrowBalance); //increase variable borrows
        } else if (_currentRateMode == CoreLibrary.InterestRateMode.VARIABLE) {
            //swap to stable
            uint256 currentStableRate = reserve.currentStableBorrowRate;
            reserve.decreaseTotalBorrowsVariable(_principalBorrowBalance);
            reserve.increaseTotalBorrowsStableAndUpdateAverageRate(
                _compoundedBorrowBalance,
                currentStableRate
            );

        } else {
            revert("Invalid rate mode received");
        }
    }

    /**
    * @dev updates the state of the user as a consequence of a swap rate action.
    * @param _reserve the address of the reserve on which the user is performing the swap
    * @param _user the address of the borrower
    * @param _balanceIncrease the accrued interest on the borrowed amount
    * @param _currentRateMode the current rate mode of the user
    **/

    function updateUserStateOnSwapRateInternal(
        address _reserve,
        address _user,
        uint256 _balanceIncrease,
        CoreLibrary.InterestRateMode _currentRateMode
    ) internal returns (CoreLibrary.InterestRateMode) {
        CoreLibrary.UserReserveData storage user = usersReserveData[_user][_reserve];
        CoreLibrary.ReserveData storage reserve = reserves[_reserve];

        CoreLibrary.InterestRateMode newMode = CoreLibrary.InterestRateMode.NONE;

        if (_currentRateMode == CoreLibrary.InterestRateMode.VARIABLE) {
            //switch to stable
            newMode = CoreLibrary.InterestRateMode.STABLE;
            user.stableBorrowRate = reserve.currentStableBorrowRate;
            user.lastVariableBorrowCumulativeIndex = 0;
        } else if (_currentRateMode == CoreLibrary.InterestRateMode.STABLE) {
            newMode = CoreLibrary.InterestRateMode.VARIABLE;
            user.stableBorrowRate = 0;
            user.lastVariableBorrowCumulativeIndex = reserve.lastVariableBorrowCumulativeIndex;
        } else {
            revert("Invalid interest rate mode received");
        }
        //compounding cumulated interest
        user.principalBorrowBalance = user.principalBorrowBalance.add(_balanceIncrease);
        //solium-disable-next-line
        user.lastUpdateTimestamp = uint40(block.timestamp);

        return newMode;
    }

    /**
    * @dev updates the state of the core as a consequence of a liquidation action.
    * @param _principalReserve the address of the principal reserve that is being repaid
    * @param _collateralReserve the address of the collateral reserve that is being liquidated
    * @param _user the address of the borrower
    * @param _amountToLiquidate the amount being repaid by the liquidator
    * @param _collateralToLiquidate the amount of collateral being liquidated
    * @param _feeLiquidated the amount of origination fee being liquidated
    * @param _liquidatedCollateralForFee the amount of collateral equivalent to the origination fee + bonus
    * @param _balanceIncrease the accrued interest on the borrowed amount
    * @param _liquidatorReceivesAToken true if the liquidator will receive aTokens, false otherwise
    **/
    function updateStateOnLiquidation(
        address _principalReserve,
        address _collateralReserve,
        address _user,
        uint256 _amountToLiquidate,
        uint256 _collateralToLiquidate,
        uint256 _feeLiquidated,
        uint256 _liquidatedCollateralForFee,
        uint256 _balanceIncrease,
        bool _liquidatorReceivesAToken
    ) external onlyLendingPool {
        updatePrincipalReserveStateOnLiquidationInternal(
            _principalReserve,
            _user,
            _amountToLiquidate,
            _balanceIncrease
        );

        updateCollateralReserveStateOnLiquidationInternal(
            _collateralReserve
        );

        updateUserStateOnLiquidationInternal(
            _principalReserve,
            _user,
            _amountToLiquidate,
            _feeLiquidated,
            _balanceIncrease
        );

        updateReserveInterestRatesAndTimestampInternal(_principalReserve, _amountToLiquidate, 0);

        if (!_liquidatorReceivesAToken) {
            updateReserveInterestRatesAndTimestampInternal(
                _collateralReserve,
                0,
                _collateralToLiquidate.add(_liquidatedCollateralForFee)
            );
        }

    }

    /**
    * @dev updates the state of the principal reserve as a consequence of a liquidation action.
    * @param _principalReserve the address of the principal reserve that is being repaid
    * @param _user the address of the borrower
    * @param _amountToLiquidate the amount being repaid by the liquidator
    * @param _balanceIncrease the accrued interest on the borrowed amount
    **/

    function updatePrincipalReserveStateOnLiquidationInternal(
        address _principalReserve,
        address _user,
        uint256 _amountToLiquidate,
        uint256 _balanceIncrease
    ) internal {
        CoreLibrary.ReserveData storage reserve = reserves[_principalReserve];
        CoreLibrary.UserReserveData storage user = usersReserveData[_user][_principalReserve];

        //update principal reserve data
        reserve.updateCumulativeIndexes();

        CoreLibrary.InterestRateMode borrowRateMode = getUserCurrentBorrowRateMode(
            _principalReserve,
            _user
        );

        if (borrowRateMode == CoreLibrary.InterestRateMode.STABLE) {
            //increase the total borrows by the compounded interest
            reserve.increaseTotalBorrowsStableAndUpdateAverageRate(
                _balanceIncrease,
                user.stableBorrowRate
            );

            //decrease by the actual amount to liquidate
            reserve.decreaseTotalBorrowsStableAndUpdateAverageRate(
                _amountToLiquidate,
                user.stableBorrowRate
            );

        } else {
            //increase the total borrows by the compounded interest
            reserve.increaseTotalBorrowsVariable(_balanceIncrease);

            //decrease by the actual amount to liquidate
            reserve.decreaseTotalBorrowsVariable(_amountToLiquidate);
        }

    }

    /**
    * @dev updates the state of the collateral reserve as a consequence of a liquidation action.
    * @param _collateralReserve the address of the collateral reserve that is being liquidated
    **/
    function updateCollateralReserveStateOnLiquidationInternal(
        address _collateralReserve
    ) internal {
        //update collateral reserve
        reserves[_collateralReserve].updateCumulativeIndexes();

    }

    /**
    * @dev updates the state of the user being liquidated as a consequence of a liquidation action.
    * @param _reserve the address of the principal reserve that is being repaid
    * @param _user the address of the borrower
    * @param _amountToLiquidate the amount being repaid by the liquidator
    * @param _feeLiquidated the amount of origination fee being liquidated
    * @param _balanceIncrease the accrued interest on the borrowed amount
    **/
    function updateUserStateOnLiquidationInternal(
        address _reserve,
        address _user,
        uint256 _amountToLiquidate,
        uint256 _feeLiquidated,
        uint256 _balanceIncrease
    ) internal {
        CoreLibrary.UserReserveData storage user = usersReserveData[_user][_reserve];
        CoreLibrary.ReserveData storage reserve = reserves[_reserve];
        //first increase by the compounded interest, then decrease by the liquidated amount
        user.principalBorrowBalance = user.principalBorrowBalance.add(_balanceIncrease).sub(
            _amountToLiquidate
        );

        if (
            getUserCurrentBorrowRateMode(_reserve, _user) == CoreLibrary.InterestRateMode.VARIABLE
        ) {
            user.lastVariableBorrowCumulativeIndex = reserve.lastVariableBorrowCumulativeIndex;
        }

        if(_feeLiquidated > 0){
            user.originationFee = user.originationFee.sub(_feeLiquidated);
        }

        //solium-disable-next-line
        user.lastUpdateTimestamp = uint40(block.timestamp);
    }

    /**
    * @dev updates the state of the core as a consequence of a stable rate rebalance
    * @param _reserve the address of the principal reserve where the user borrowed
    * @param _user the address of the borrower
    * @param _balanceIncrease the accrued interest on the borrowed amount
    * @return the new stable rate for the user
    **/
    function updateStateOnRebalance(address _reserve, address _user, uint256 _balanceIncrease)
        external
        onlyLendingPool
        returns (uint256)
    {
        updateReserveStateOnRebalanceInternal(_reserve, _user, _balanceIncrease);

        //update user data and rebalance the rate
        updateUserStateOnRebalanceInternal(_reserve, _user, _balanceIncrease);
        updateReserveInterestRatesAndTimestampInternal(_reserve, 0, 0);
        return usersReserveData[_user][_reserve].stableBorrowRate;
    }

    /**
    * @dev updates the state of the reserve as a consequence of a stable rate rebalance
    * @param _reserve the address of the principal reserve where the user borrowed
    * @param _user the address of the borrower
    * @param _balanceIncrease the accrued interest on the borrowed amount
    **/

    function updateReserveStateOnRebalanceInternal(
        address _reserve,
        address _user,
        uint256 _balanceIncrease
    ) internal {
        CoreLibrary.ReserveData storage reserve = reserves[_reserve];
        CoreLibrary.UserReserveData storage user = usersReserveData[_user][_reserve];

        reserve.updateCumulativeIndexes();

        reserve.increaseTotalBorrowsStableAndUpdateAverageRate(
            _balanceIncrease,
            user.stableBorrowRate
        );

    }

    /**
    * @dev updates the state of the user as a consequence of a stable rate rebalance
    * @param _reserve the address of the principal reserve where the user borrowed
    * @param _user the address of the borrower
    * @param _balanceIncrease the accrued interest on the borrowed amount
    **/

    function updateUserStateOnRebalanceInternal(
        address _reserve,
        address _user,
        uint256 _balanceIncrease
    ) internal {
        CoreLibrary.UserReserveData storage user = usersReserveData[_user][_reserve];
        CoreLibrary.ReserveData storage reserve = reserves[_reserve];

        user.principalBorrowBalance = user.principalBorrowBalance.add(_balanceIncrease);
        user.stableBorrowRate = reserve.currentStableBorrowRate;

        //solium-disable-next-line
        user.lastUpdateTimestamp = uint40(block.timestamp);
    }

    struct AvailableCollateralToLiquidateLocalVars {
        uint256 userCompoundedBorrowBalance;
        uint256 liquidationBonus;
        uint256 collateralPrice;
        uint256 principalCurrencyPrice;
        uint256 maxAmountCollateralToLiquidate;
    }
    /**
    * @dev calculates how much of a specific collateral can be liquidated, given
    * a certain amount of principal currency. This function needs to be called after
    * all the checks to validate the liquidation have been performed, otherwise it might fail.
    * @param _collateral the collateral to be liquidated
    * @param _principal the principal currency to be liquidated
    * @param _purchaseAmount the amount of principal being liquidated
    * @param _userCollateralBalance the collatera balance for the specific _collateral asset of the user being liquidated
    * @return the maximum amount that is possible to liquidated given all the liquidation constraints (user balance, close factor) and
    * the purchase amount
    **/
    function calculateAvailableCollateralToLiquidate(
        address _collateral,
        address _principal,
        uint256 _purchaseAmount,
        uint256 _userCollateralBalance
    ) internal view returns (uint256 collateralAmount, uint256 principalAmountNeeded) {
        collateralAmount = 0;
        principalAmountNeeded = 0;
        IPriceOracleGetter oracle = IPriceOracleGetter(addressesProvider.getPriceOracle());

        // Usage of a memory struct of vars to avoid "Stack too deep" errors due to local variables
        AvailableCollateralToLiquidateLocalVars memory vars;

        vars.collateralPrice = oracle.getAssetPrice(_collateral);
        vars.principalCurrencyPrice = oracle.getAssetPrice(_principal);
        vars.liquidationBonus = core.getReserveLiquidationBonus(_collateral);

        //this is the maximum possible amount of the selected collateral that can be liquidated, given the
        //max amount of principal currency that is available for liquidation.
        vars.maxAmountCollateralToLiquidate = vars
            .principalCurrencyPrice
            .mul(_purchaseAmount)
            .div(vars.collateralPrice)
            .mul(vars.liquidationBonus)
            .div(100);

        if (vars.maxAmountCollateralToLiquidate > _userCollateralBalance) {
            collateralAmount = _userCollateralBalance;
            principalAmountNeeded = vars
                .collateralPrice
                .mul(collateralAmount)
                .div(vars.principalCurrencyPrice)
                .mul(100)
                .div(vars.liquidationBonus);
        } else {
            collateralAmount = vars.maxAmountCollateralToLiquidate;
            principalAmountNeeded = _purchaseAmount;
        }

        return (collateralAmount, principalAmountNeeded);
    }
}

    struct LiquidationCallLocalVars {
        uint256 userCollateralBalance;
        uint256 userCompoundedBorrowBalance;
        uint256 borrowBalanceIncrease;
        uint256 maxPrincipalAmountToLiquidate;
        uint256 actualAmountToLiquidate;
        uint256 liquidationRatio;
        uint256 collateralPrice;
        uint256 principalCurrencyPrice;
        uint256 maxAmountCollateralToLiquidate;
        uint256 originationFee;
        uint256 feeLiquidated;
        uint256 liquidatedCollateralForFee;
        CoreLibrary.InterestRateMode borrowRateMode;
        uint256 userStableRate;
        bool isCollateralEnabled;
        bool healthFactorBelowThreshold;
    }

        LiquidationCallLocalVars memory vars;

        (, , , , , , , vars.healthFactorBelowThreshold) = dataProvider.calculateUserGlobalData(
            _user
        );

        if (!vars.healthFactorBelowThreshold) {
            return (
                uint256(LiquidationErrors.HEALTH_FACTOR_ABOVE_THRESHOLD),
                "Health factor is not below the threshold"
            );
        }

        vars.userCollateralBalance = core.getUserUnderlyingAssetBalance(_collateral, _user);

        //if _user hasn't deposited this specific collateral, nothing can be liquidated
        if (vars.userCollateralBalance == 0) {
            return (
                uint256(LiquidationErrors.NO_COLLATERAL_AVAILABLE),
                "Invalid collateral to liquidate"
            );
        }

        vars.isCollateralEnabled =
            core.isReserveUsageAsCollateralEnabled(_collateral) &&
            core.isUserUseReserveAsCollateralEnabled(_collateral, _user);

        //if _collateral isn't enabled as collateral by _user, it cannot be liquidated
        if (!vars.isCollateralEnabled) {
            return (
                uint256(LiquidationErrors.COLLATERAL_CANNOT_BE_LIQUIDATED),
                "The collateral chosen cannot be liquidated"
            );
        }

        //if the user hasn't borrowed the specific currency defined by _reserve, it cannot be liquidated
        (, vars.userCompoundedBorrowBalance, vars.borrowBalanceIncrease) = core
            .getUserBorrowBalances(_reserve, _user);

        if (vars.userCompoundedBorrowBalance == 0) {
            return (
                uint256(LiquidationErrors.CURRRENCY_NOT_BORROWED),
                "User did not borrow the specified currency"
            );
        }

        //all clear - calculate the max principal amount that can be liquidated
        vars.maxPrincipalAmountToLiquidate = vars
            .userCompoundedBorrowBalance
            .mul(LIQUIDATION_CLOSE_FACTOR_PERCENT)
            .div(100);

        vars.actualAmountToLiquidate = _purchaseAmount > vars.maxPrincipalAmountToLiquidate
            ? vars.maxPrincipalAmountToLiquidate
            : _purchaseAmount;

        (uint256 maxCollateralToLiquidate, uint256 principalAmountNeeded) = calculateAvailableCollateralToLiquidate(
            _collateral,
            _reserve,
            vars.actualAmountToLiquidate,
            vars.userCollateralBalance
        );
        vars.originationFee = core.getUserOriginationFee(_reserve, _user);

        //if there is a fee to liquidate, calculate the maximum amount of fee that can be liquidated
        if (vars.originationFee > 0) {
            (
                vars.liquidatedCollateralForFee,
                vars.feeLiquidated
            ) = calculateAvailableCollateralToLiquidate(
                _collateral,
                _reserve,
                vars.originationFee,
                vars.userCollateralBalance.sub(maxCollateralToLiquidate)
            );
        }
        //if principalAmountNeeded < vars.ActualAmountToLiquidate, there isn't enough
        //of _collateral to cover the actual amount that is being liquidated, hence we liquidate
        //a smaller amount

        if (principalAmountNeeded < vars.actualAmountToLiquidate) {
            vars.actualAmountToLiquidate = principalAmountNeeded;
        }

        //if liquidator reclaims the underlying asset, we make sure there is enough available collateral in the reserve
        if (!_receiveAToken) {
            uint256 currentAvailableCollateral = core.getReserveAvailableLiquidity(_collateral);
            if (currentAvailableCollateral < maxCollateralToLiquidate) {
                return (
                    uint256(LiquidationErrors.NOT_ENOUGH_LIQUIDITY),
                    "There isn't enough liquidity available to liquidate"
                );
            }
        }

        core.updateStateOnLiquidation(
            _reserve,
            _collateral,
            _user,
            vars.actualAmountToLiquidate,
            maxCollateralToLiquidate,
            vars.feeLiquidated,
            vars.liquidatedCollateralForFee,
            vars.borrowBalanceIncrease,
            _receiveAToken
        );

        AToken collateralAtoken = AToken(core.getReserveATokenAddress(_collateral));

        //if liquidator reclaims the aToken, he receives the equivalent atoken amount
        if (_receiveAToken) {
            collateralAtoken.transferOnLiquidation(_user, msg.sender, maxCollateralToLiquidate);
        } else {
            //otherwise receives the underlying asset
            //burn the equivalent amount of atoken
            collateralAtoken.burnOnLiquidation(_user, maxCollateralToLiquidate);
            core.transferToUser(_collateral, msg.sender, maxCollateralToLiquidate);
        }

        //transfers the principal currency to the pool
        core.transferToReserve.value(msg.value)(_reserve, msg.sender, vars.actualAmountToLiquidate);

        if (vars.feeLiquidated > 0) {
            //if there is enough collateral to liquidate the fee, first transfer burn an equivalent amount of
            //aTokens of the user
            collateralAtoken.burnOnLiquidation(_user, vars.liquidatedCollateralForFee);

            //then liquidate the fee by transferring it to the fee collection address
            core.liquidateFee(
                _collateral,
                vars.liquidatedCollateralForFee,
                addressesProvider.getTokenDistributor()
            );

            emit OriginationFeeLiquidated(
                _collateral,
                _reserve,
                _user,
                vars.feeLiquidated,
                vars.liquidatedCollateralForFee,
                //solium-disable-next-line
                block.timestamp
            );

        }

    struct UserReserveData {
        //principal amount borrowed by the user.
        uint256 principalBorrowBalance;
        //cumulated variable borrow index for the user. Expressed in ray
        uint256 lastVariableBorrowCumulativeIndex;
        //origination fee cumulated by the user
        uint256 originationFee;
        // stable borrow rate at which the user has borrowed. Expressed in ray
        uint256 stableBorrowRate;
        uint40 lastUpdateTimestamp;
        //defines if a specific deposit should or not be used as a collateral in borrows
        bool useAsCollateral;
    }

    struct ReserveData {
        /**
        * @dev refer to the whitepaper, section 1.1 basic concepts for a formal description of these properties.
        **/
        //the liquidity index. Expressed in ray
        uint256 lastLiquidityCumulativeIndex;
        //the current supply rate. Expressed in ray
        uint256 currentLiquidityRate;
        //the total borrows of the reserve at a stable rate. Expressed in the currency decimals
        uint256 totalBorrowsStable;
        //the total borrows of the reserve at a variable rate. Expressed in the currency decimals
        uint256 totalBorrowsVariable;
        //the current variable borrow rate. Expressed in ray
        uint256 currentVariableBorrowRate;
        //the current stable borrow rate. Expressed in ray
        uint256 currentStableBorrowRate;
        //the current average stable borrow rate (weighted average of all the different stable rate loans). Expressed in ray
        uint256 currentAverageStableBorrowRate;
        //variable borrow index. Expressed in ray
        uint256 lastVariableBorrowCumulativeIndex;
        //the ltv of the reserve. Expressed in percentage (0-100)
        uint256 baseLTVasCollateral;
        //the liquidation threshold of the reserve. Expressed in percentage (0-100)
        uint256 liquidationThreshold;
        //the liquidation bonus of the reserve. Expressed in percentage
        uint256 liquidationBonus;
        //the decimals of the reserve asset
        uint256 decimals;
        /**
        * @dev address of the aToken representing the asset
        **/
        address aTokenAddress;
        /**
        * @dev address of the interest rate strategy contract
        **/
        address interestRateStrategyAddress;
        uint40 lastUpdateTimestamp;
        // borrowingEnabled = true means users can borrow from this reserve
        bool borrowingEnabled;
        // usageAsCollateralEnabled = true means users can use this reserve as collateral
        bool usageAsCollateralEnabled;
        // isStableBorrowRateEnabled = true means users can borrow at a stable rate
        bool isStableBorrowRateEnabled;
        // isActive = true means the reserve has been activated and properly configured
        bool isActive;
        // isFreezed = true means the reserve only allows repays and redeems, but not deposits, new borrowings or rate swap
        bool isFreezed;
    }

    /**
    * @dev function to calculate the interest using a compounded interest rate formula
    * @param _rate the interest rate, in ray
    * @param _lastUpdateTimestamp the timestamp of the last update of the interest
    * @return the interest rate compounded during the timeDelta, in ray
    **/
    function calculateCompoundedInterest(uint256 _rate, uint40 _lastUpdateTimestamp)
        internal
        view
        returns (uint256)
    {
        //solium-disable-next-line
        uint256 timeDifference = block.timestamp.sub(uint256(_lastUpdateTimestamp));

        uint256 ratePerSecond = _rate.div(SECONDS_PER_YEAR);

        return ratePerSecond.add(WadRayMath.ray()).rayPow(timeDifference);
    }

    function calculateLinearInterest(uint256 _rate, uint40 _lastUpdateTimestamp)
        internal
        view
        returns (uint256)
    {
        //solium-disable-next-line
        uint256 timeDifference = block.timestamp.sub(uint256(_lastUpdateTimestamp));

        uint256 timeDelta = timeDifference.wadToRay().rayDiv(SECONDS_PER_YEAR.wadToRay());

        return _rate.rayMul(timeDelta).add(WadRayMath.ray());
    }

/**
    * @dev Updates the liquidity cumulative index Ci and variable borrow cumulative index Bvc. Refer to the whitepaper for
    * a formal specification.
    * @param _self the reserve object
    **/
    function updateCumulativeIndexes(ReserveData storage _self) internal {
        uint256 totalBorrows = getTotalBorrows(_self);

        if (totalBorrows > 0) {
            //only cumulating if there is any income being produced
            uint256 cumulatedLiquidityInterest = calculateLinearInterest(
                _self.currentLiquidityRate,
                _self.lastUpdateTimestamp
            );

            _self.lastLiquidityCumulativeIndex = cumulatedLiquidityInterest.rayMul(
                _self.lastLiquidityCumulativeIndex
            );

            uint256 cumulatedVariableBorrowInterest = calculateCompoundedInterest(
                _self.currentVariableBorrowRate,
                _self.lastUpdateTimestamp
            );
            _self.lastVariableBorrowCumulativeIndex = cumulatedVariableBorrowInterest.rayMul(
                _self.lastVariableBorrowCumulativeIndex
            );
        }
    }

    /**
    * @dev accumulates a predefined amount of asset to the reserve as a fixed, one time income. Used for example to accumulate
    * the flashloan fee to the reserve, and spread it through the depositors.
    * @param _self the reserve object
    * @param _totalLiquidity the total liquidity available in the reserve
    * @param _amount the amount to accomulate
    **/
    function cumulateToLiquidityIndex(
        ReserveData storage _self,
        uint256 _totalLiquidity,
        uint256 _amount
    ) internal {
        uint256 amountToLiquidityRatio = _amount.wadToRay().rayDiv(_totalLiquidity.wadToRay());

        uint256 cumulatedLiquidity = amountToLiquidityRatio.add(WadRayMath.ray());

        _self.lastLiquidityCumulativeIndex = cumulatedLiquidity.rayMul(
            _self.lastLiquidityCumulativeIndex
        );
    }

    /**
    * @dev increases the total borrows at a stable rate on a specific reserve and updates the
    * average stable rate consequently
    * @param _reserve the reserve object
    * @param _amount the amount to add to the total borrows stable
    * @param _rate the rate at which the amount has been borrowed
    **/
    function increaseTotalBorrowsStableAndUpdateAverageRate(
        ReserveData storage _reserve,
        uint256 _amount,
        uint256 _rate
    ) internal {
        uint256 previousTotalBorrowStable = _reserve.totalBorrowsStable;
        //updating reserve borrows stable
        _reserve.totalBorrowsStable = _reserve.totalBorrowsStable.add(_amount);

        //update the average stable rate
        //weighted average of all the borrows
        uint256 weightedLastBorrow = _amount.wadToRay().rayMul(_rate);
        uint256 weightedPreviousTotalBorrows = previousTotalBorrowStable.wadToRay().rayMul(
            _reserve.currentAverageStableBorrowRate
        );

        _reserve.currentAverageStableBorrowRate = weightedLastBorrow
            .add(weightedPreviousTotalBorrows)
            .rayDiv(_reserve.totalBorrowsStable.wadToRay());
    }

    /**
    * @dev decreases the total borrows at a stable rate on a specific reserve and updates the
    * average stable rate consequently
    * @param _reserve the reserve object
    * @param _amount the amount to substract to the total borrows stable
    * @param _rate the rate at which the amount has been repaid
    **/
    function decreaseTotalBorrowsStableAndUpdateAverageRate(
        ReserveData storage _reserve,
        uint256 _amount,
        uint256 _rate
    ) internal {
        require(_reserve.totalBorrowsStable >= _amount, "Invalid amount to decrease");

        uint256 previousTotalBorrowStable = _reserve.totalBorrowsStable;

        //updating reserve borrows stable
        _reserve.totalBorrowsStable = _reserve.totalBorrowsStable.sub(_amount);

        if (_reserve.totalBorrowsStable == 0) {
            _reserve.currentAverageStableBorrowRate = 0; //no income if there are no stable rate borrows
            return;
        }

        //update the average stable rate
        //weighted average of all the borrows
        uint256 weightedLastBorrow = _amount.wadToRay().rayMul(_rate);
        uint256 weightedPreviousTotalBorrows = previousTotalBorrowStable.wadToRay().rayMul(
            _reserve.currentAverageStableBorrowRate
        );

        require(
            weightedPreviousTotalBorrows >= weightedLastBorrow,
            "The amounts to subtract don't match"
        );

        _reserve.currentAverageStableBorrowRate = weightedPreviousTotalBorrows
            .sub(weightedLastBorrow)
            .rayDiv(_reserve.totalBorrowsStable.wadToRay());
    }

    /**
    * @dev increases the total borrows at a variable rate
    * @param _reserve the reserve object
    * @param _amount the amount to add to the total borrows variable
    **/
    function increaseTotalBorrowsVariable(ReserveData storage _reserve, uint256 _amount) internal {
        _reserve.totalBorrowsVariable = _reserve.totalBorrowsVariable.add(_amount);
    }

    /**
    * @dev decreases the total borrows at a variable rate
    * @param _reserve the reserve object
    * @param _amount the amount to substract to the total borrows variable
    **/
    function decreaseTotalBorrowsVariable(ReserveData storage _reserve, uint256 _amount) internal {
        require(
            _reserve.totalBorrowsVariable >= _amount,
            "The amount that is being subtracted from the variable total borrows is incorrect"
        );
        _reserve.totalBorrowsVariable = _reserve.totalBorrowsVariable.sub(_amount);
    }

    /**
    * @dev returns the principal balance of the user. The principal balance is the last
    * updated stored balance, which does not consider the perpetually accruing interest.
    * @param _user the address of the user
    * @return the principal balance of the user
    **/
    function principalBalanceOf(address _user) external view returns(uint256) {
        return super.balanceOf(_user);
    }
    /**
    * @dev calculates the balance of the user, which is the
    * principal balance + interest generated by the principal balance + interest generated by the redirected balance
    * @param _user the user for which the balance is being calculated
    * @return the total balance of the user
    **/
    function balanceOf(address _user) public view returns(uint256) {

        //current principal balance of the user
        uint256 currentPrincipalBalance = super.balanceOf(_user);
        //balance redirected by other users to _user for interest rate accrual
        uint256 redirectedBalance = redirectedBalances[_user];

        if(currentPrincipalBalance == 0 && redirectedBalance == 0){
            return 0;
        }
        //if the _user is not redirecting the interest to anybody, accrues
        //the interest for himself

        if(interestRedirectionAddresses[_user] == address(0)){

            //accruing for himself means that both the principal balance and
            //the redirected balance partecipate in the interest
            return calculateCumulatedBalanceInternal(
                _user,
                currentPrincipalBalance.add(redirectedBalance)
                )
                .sub(redirectedBalance);
        }
        else {
            //if the user redirected the interest, then only the redirected
            //balance generates interest. In that case, the interest generated
            //by the redirected balance is added to the current principal balance.
            return currentPrincipalBalance.add(
                calculateCumulatedBalanceInternal(
                    _user,
                    redirectedBalance
                )
                .sub(redirectedBalance)
            );
        }
    }

address public underlyingAssetAddress;

    mapping (address => uint256) private userIndexes;
    mapping (address => address) private interestRedirectionAddresses;
    mapping (address => uint256) private redirectedBalances;
    mapping (address => address) private interestRedirectionAllowances;

    LendingPoolAddressesProvider private addressesProvider;
    LendingPoolCore private core;
    LendingPool private pool;
    LendingPoolDataProvider private dataProvider;

    /**
    * @dev redirects the interest generated to a target address.
    * when the interest is redirected, the user balance is added to
    * the recepient redirected balance.
    * @param _to the address to which the interest will be redirected
    **/
    function redirectInterestStream(address _to) external {
        redirectInterestStreamInternal(msg.sender, _to);
    }
    
    ...
    /**
    * @dev executes the redirection of the interest from one address to another.
    * immediately after redirection, the destination address will start to accrue interest.
    * @param _from the address from which transfer the aTokens
    * @param _to the destination address
    **/
    function redirectInterestStreamInternal(
        address _from,
        address _to
    ) internal {

        address currentRedirectionAddress = interestRedirectionAddresses[_from];

        require(_to != currentRedirectionAddress, "Interest is already redirected to the user");

        //accumulates the accrued interest to the principal
        (uint256 previousPrincipalBalance,
        uint256 fromBalance,
        uint256 balanceIncrease,
        uint256 fromIndex) = cumulateBalanceInternal(_from);

        require(fromBalance > 0, "Interest stream can only be redirected if there is a valid balance");

        //if the user is already redirecting the interest to someone, before changing
        //the redirection address we substract the redirected balance of the previous
        //recipient
        if(currentRedirectionAddress != address(0)){
            updateRedirectedBalanceOfRedirectionAddressInternal(_from,0, previousPrincipalBalance);
        }

        //if the user is redirecting the interest back to himself,
        //we simply set to 0 the interest redirection address
        if(_to == _from) {
            interestRedirectionAddresses[_from] = address(0);
            emit InterestStreamRedirected(
                _from,
                address(0),
                fromBalance,
                balanceIncrease,
                fromIndex
            );
            return;
        }

        //first set the redirection address to the new recipient
        interestRedirectionAddresses[_from] = _to;

        //adds the user balance to the redirected balance of the destination
        updateRedirectedBalanceOfRedirectionAddressInternal(_from,fromBalance,0);

        emit InterestStreamRedirected(
            _from,
            _to,
            fromBalance,
            balanceIncrease,
            fromIndex
        );
    }

    /**
    * @dev accumulates the accrued interest of the user to the principal balance
    * @param _user the address of the user for which the interest is being accumulated
    * @return the previous principal balance, the new principal balance, the balance increase
    * and the new user index
    **/
    function cumulateBalanceInternal(address _user)
        internal
        returns(uint256, uint256, uint256, uint256) {

        uint256 previousPrincipalBalance = super.balanceOf(_user);

        //calculate the accrued interest since the last accumulation
        uint256 balanceIncrease = balanceOf(_user).sub(previousPrincipalBalance);
        //mints an amount of tokens equivalent to the amount accumulated
        _mint(_user, balanceIncrease);
        //updates the user index
        uint256 index = userIndexes[_user] = core.getReserveNormalizedIncome(underlyingAssetAddress);
        return (
            previousPrincipalBalance,
            previousPrincipalBalance.add(balanceIncrease),
            balanceIncrease,
            index
        );
    }

    /**
    * @dev updates the redirected balance of the user. If the user is not redirecting his
    * interest, nothing is executed.
    * @param _user the address of the user for which the interest is being accumulated
    * @param _balanceToAdd the amount to add to the redirected balance
    * @param _balanceToRemove the amount to remove from the redirected balance
    **/
    function updateRedirectedBalanceOfRedirectionAddressInternal(
        address _user,
        uint256 _balanceToAdd,
        uint256 _balanceToRemove
    ) internal {

        address redirectionAddress = interestRedirectionAddresses[_user];
        //if there isn't any redirection, nothing to be done
        if(redirectionAddress == address(0)){
            return;
        }

        //compound balances of the redirected address
        (,,uint256 balanceIncrease, uint256 index) = cumulateBalanceInternal(redirectionAddress);

        //updating the redirected balance
        redirectedBalances[redirectionAddress] = redirectedBalances[redirectionAddress]
            .add(_balanceToAdd)
            .sub(_balanceToRemove);

        //if the interest of redirectionAddress is also being redirected, we need to update
        //the redirected balance of the redirection target by adding the balance increase
        address targetOfRedirectionAddress = interestRedirectionAddresses[redirectionAddress];

        if(targetOfRedirectionAddress != address(0)){
            redirectedBalances[targetOfRedirectionAddress] = redirectedBalances[targetOfRedirectionAddress].add(balanceIncrease);
        }

        emit RedirectedBalanceUpdated(
            redirectionAddress,
            balanceIncrease,
            index,
            _balanceToAdd,
            _balanceToRemove
        );
    }

    /**
    * @dev gives allowance to an address to execute the interest redirection
    * on behalf of the caller.
    * @param _to the address to which the interest will be redirected. Pass address(0) to reset
    * the allowance.
    **/
    function allowInterestRedirectionTo(address _to) external {
        require(_to != msg.sender, "User cannot give allowance to himself");
        interestRedirectionAllowances[msg.sender] = _to;
        emit InterestRedirectionAllowanceChanged(
            msg.sender,
            _to
        );
    }

    /**
    * @dev redeems aToken for the underlying asset
    * @param _amount the amount being redeemed
    **/
    function redeem(uint256 _amount) external {

        require(_amount > 0, "Amount to redeem needs to be > 0");

        //cumulates the balance of the user
        (,
        uint256 currentBalance,
        uint256 balanceIncrease,
        uint256 index) = cumulateBalanceInternal(msg.sender);

        uint256 amountToRedeem = _amount;

        //if amount is equal to uint(-1), the user wants to redeem everything
        if(_amount == UINT_MAX_VALUE){
            amountToRedeem = currentBalance;
        }

        require(amountToRedeem <= currentBalance, "User cannot redeem more than the available balance");

        //check that the user is allowed to redeem the amount
        require(isTransferAllowed(msg.sender, amountToRedeem), "Transfer cannot be allowed.");

        //if the user is redirecting his interest towards someone else,
        //we update the redirected balance of the redirection address by adding the accrued interest,
        //and removing the amount to redeem
        updateRedirectedBalanceOfRedirectionAddressInternal(msg.sender, balanceIncrease, amountToRedeem);

        // burns tokens equivalent to the amount requested
        _burn(msg.sender, amountToRedeem);

        bool userIndexReset = false;
        //reset the user data if the remaining balance is 0
        if(currentBalance.sub(amountToRedeem) == 0){
            userIndexReset = resetDataOnZeroBalanceInternal(msg.sender);
        }

        // executes redeem of the underlying asset
        pool.redeemUnderlying(
            underlyingAssetAddress,
            msg.sender,
            amountToRedeem,
            currentBalance.sub(amountToRedeem)
        );

        emit Redeem(msg.sender, amountToRedeem, balanceIncrease, userIndexReset ? 0 : index);
    }

    /**
    * @dev function to reset the interest stream redirection and the user index, if the
    * user has no balance left.
    * @param _user the address of the user
    * @return true if the user index has also been reset, false otherwise. useful to emit the proper user index value
    **/
    function resetDataOnZeroBalanceInternal(address _user) internal returns(bool) {

        //if the user has 0 principal balance, the interest stream redirection gets reset
        interestRedirectionAddresses[_user] = address(0);

        //emits a InterestStreamRedirected event to notify that the redirection has been reset
        emit InterestStreamRedirected(_user, address(0),0,0,0);

        //if the redirected balance is also 0, we clear up the user index
        if(redirectedBalances[_user] == 0){
            userIndexes[_user] = 0;
            return true;
        }
        else{
            return false;
        }
    }

    /**
     * @dev mints token in the event of users depositing the underlying asset into the lending pool
     * only lending pools can call this function
     * @param _account the address receiving the minted tokens
     * @param _amount the amount of tokens to mint
     */
    function mintOnDeposit(address _account, uint256 _amount) external onlyLendingPool {

        //cumulates the balance of the user
        (,
        ,
        uint256 balanceIncrease,
        uint256 index) = cumulateBalanceInternal(_account);

         //if the user is redirecting his interest towards someone else,
        //we update the redirected balance of the redirection address by adding the accrued interest
        //and the amount deposited
        updateRedirectedBalanceOfRedirectionAddressInternal(_account, balanceIncrease.add(_amount), 0);

        //mint an equivalent amount of tokens to cover the new deposit
        _mint(_account, _amount);

        emit MintOnDeposit(_account, _amount, balanceIncrease, index);
    }

    /**
     * @dev burns token in the event of a borrow being liquidated, in case the liquidators reclaims the underlying asset
     * Transfer of the liquidated asset is executed by the lending pool contract.
     * only lending pools can call this function
     * @param _account the address from which burn the aTokens
     * @param _value the amount to burn
     **/
    function burnOnLiquidation(address _account, uint256 _value) external onlyLendingPool {

        //cumulates the balance of the user being liquidated
        (,uint256 accountBalance,uint256 balanceIncrease,uint256 index) = cumulateBalanceInternal(_account);

        //adds the accrued interest and substracts the burned amount to
        //the redirected balance
        updateRedirectedBalanceOfRedirectionAddressInternal(_account, balanceIncrease, _value);

        //burns the requested amount of tokens
        _burn(_account, _value);

        bool userIndexReset = false;
        //reset the user data if the remaining balance is 0
        if(accountBalance.sub(_value) == 0){
            userIndexReset = resetDataOnZeroBalanceInternal(_account);
        }

        emit BurnOnLiquidation(_account, _value, balanceIncrease, userIndexReset ? 0 : index);
    }
    /**
     * @dev transfers tokens in the event of a borrow being liquidated, in case the liquidators reclaims the aToken
     *      only lending pools can call this function
     * @param _from the address from which transfer the aTokens
     * @param _to the destination address
     * @param _value the amount to transfer
     **/
    function transferOnLiquidation(address _from, address _to, uint256 _value) external onlyLendingPool {

        //being a normal transfer, the Transfer() and BalanceTransfer() are emitted
        //so no need to emit a specific event here
        executeTransferInternal(_from, _to, _value);
    }

    /**
    * @dev executes the transfer of aTokens, invoked by both _transfer() and
    *      transferOnLiquidation()
    * @param _from the address from which transfer the aTokens
    * @param _to the destination address
    * @param _value the amount to transfer
    **/
    function executeTransferInternal(
        address _from,
        address _to,
        uint256 _value
    ) internal {

        require(_value > 0, "Transferred amount needs to be greater than zero");

        //cumulate the balance of the sender
        (,
        uint256 fromBalance,
        uint256 fromBalanceIncrease,
        uint256 fromIndex
        ) = cumulateBalanceInternal(_from);

        //cumulate the balance of the receiver
        (,
        ,
        uint256 toBalanceIncrease,
        uint256 toIndex
        ) = cumulateBalanceInternal(_to);

        //if the sender is redirecting his interest towards someone else,
        //adds to the redirected balance the accrued interest and removes the amount
        //being transferred
        updateRedirectedBalanceOfRedirectionAddressInternal(_from, fromBalanceIncrease, _value);

        //if the receiver is redirecting his interest towards someone else,
        //adds to the redirected balance the accrued interest and the amount
        //being transferred
        updateRedirectedBalanceOfRedirectionAddressInternal(_to, toBalanceIncrease.add(_value), 0);

        //performs the transfer
        super._transfer(_from, _to, _value);

        bool fromIndexReset = false;
        //reset the user data if the remaining balance is 0
        if(fromBalance.sub(_value) == 0){
            fromIndexReset = resetDataOnZeroBalanceInternal(_from);
        }

        emit BalanceTransfer(
            _from,
            _to,
            _value,
            fromBalanceIncrease,
            toBalanceIncrease,
            fromIndexReset ? 0 : fromIndex,
            toIndex
        );
    }

  struct ReserveData {
    //stores the reserve configuration
    ReserveConfigurationMap configuration;
    //the liquidity index. Expressed in ray
    uint128 liquidityIndex;
    //variable borrow index. Expressed in ray
    uint128 variableBorrowIndex;
    //the current supply rate. Expressed in ray
    uint128 currentLiquidityRate;
    //the current variable borrow rate. Expressed in ray
    uint128 currentVariableBorrowRate;
    //the current stable borrow rate. Expressed in ray
    uint128 currentStableBorrowRate;
    uint40 lastUpdateTimestamp;
    //tokens addresses
    address aTokenAddress;
    address stableDebtTokenAddress;
    address variableDebtTokenAddress;
    //address of the interest rate strategy
    address interestRateStrategyAddress;
    //the id of the reserve. Represents the position in the list of the active reserves
    uint8 id;
  }

  struct ReserveConfigurationMap {
    //bit 0-15: LTV
    //bit 16-31: Liq. threshold
    //bit 32-47: Liq. bonus
    //bit 48-55: Decimals
    //bit 56: Reserve is active
    //bit 57: reserve is frozen
    //bit 58: borrowing is enabled
    //bit 59: stable rate borrowing enabled
    //bit 60-63: reserved
    //bit 64-79: reserve factor
    uint256 data;
  }

  struct UserConfigurationMap {
    uint256 data;
  }

  enum InterestRateMode {NONE, STABLE, VARIABLE}

	uint256 constant LTV_MASK =                   0xFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFF0000; // prettier-ignore
  /**
   * @dev Sets the Loan to Value of the reserve
   * @param self The reserve configuration
   * @param ltv the new ltv
   **/
  function setLtv(DataTypes.ReserveConfigurationMap memory self, uint256 ltv) internal pure {
    require(ltv <= MAX_VALID_LTV, Errors.RC_INVALID_LTV);

    self.data = (self.data & LTV_MASK) | ltv;
  }

  /**
   * @dev Gets the Loan to Value of the reserve
   * @param self The reserve configuration
   * @return The loan to value
   **/
  function getLtv(DataTypes.ReserveConfigurationMap storage self) internal view returns (uint256) {
    return self.data & ~LTV_MASK;
  }

  uint256 internal constant BORROWING_MASK =
    0x5555555555555555555555555555555555555555555555555555555555555555; // 010101010101.....01
  /**
   * @dev Sets if the user is using as collateral the reserve identified by reserveIndex
   * @param self The configuration object
   * @param reserveIndex The index of the reserve in the bitmap
   * @param usingAsCollateral True if the user is usin the reserve as collateral, false otherwise
   **/
  function setUsingAsCollateral(
    DataTypes.UserConfigurationMap storage self,
    uint256 reserveIndex,
    bool usingAsCollateral
  ) internal {
    require(reserveIndex < 128, Errors.UL_INVALID_INDEX);
    self.data =
      (self.data & ~(1 << (reserveIndex * 2 + 1))) |
      (uint256(usingAsCollateral ? 1 : 0) << (reserveIndex * 2 + 1));
  }
  /**
   * @dev Used to validate if a user has been borrowing from any reserve
   * @param self The configuration object
   * @return True if the user has been borrowing any reserve, false otherwise
   **/
  function isBorrowingAny(DataTypes.UserConfigurationMap memory self) internal pure returns (bool) {
    return self.data & BORROWING_MASK != 0;
  }

  /**
   * @dev Function to calculate the interest using a compounded interest rate formula
   * To avoid expensive exponentiation, the calculation is performed using a binomial approximation:
   *
   *  (1+x)^n = 1+n*x+[n/2*(n-1)]*x^2+[n/6*(n-1)*(n-2)*x^3...
   *
   * The approximation slightly underpays liquidity providers and undercharges borrowers, with the advantage of great gas cost reductions
   * The whitepaper contains reference to the approximation and a table showing the margin of error per different time periods
   *
   * @param rate The interest rate, in ray
   * @param lastUpdateTimestamp The timestamp of the last update of the interest
   * @return The interest rate compounded during the timeDelta, in ray
   **/
  function calculateCompoundedInterest(
    uint256 rate,
    uint40 lastUpdateTimestamp,
    uint256 currentTimestamp
  ) internal pure returns (uint256) {
    //solium-disable-next-line
    uint256 exp = currentTimestamp.sub(uint256(lastUpdateTimestamp));

    if (exp == 0) {
      return WadRayMath.ray();
    }

    uint256 expMinusOne = exp - 1;

    uint256 expMinusTwo = exp > 2 ? exp - 2 : 0;

    uint256 ratePerSecond = rate / SECONDS_PER_YEAR;

    uint256 basePowerTwo = ratePerSecond.rayMul(ratePerSecond);
    uint256 basePowerThree = basePowerTwo.rayMul(ratePerSecond);

    uint256 secondTerm = exp.mul(expMinusOne).mul(basePowerTwo) / 2;
    uint256 thirdTerm = exp.mul(expMinusOne).mul(expMinusTwo).mul(basePowerThree) / 6;

    return WadRayMath.ray().add(ratePerSecond.mul(exp)).add(secondTerm).add(thirdTerm);
  }

  /**
   * @dev Returns the ongoing normalized income for the reserve
   * A value of 1e27 means there is no income. As time passes, the income is accrued
   * A value of 2*1e27 means for each unit of asset one unit of income has been accrued
   * @param reserve The reserve object
   * @return the normalized income. expressed in ray
   **/
  function getNormalizedIncome(DataTypes.ReserveData storage reserve)
    internal
    view
    returns (uint256)
  {
    uint40 timestamp = reserve.lastUpdateTimestamp;

    //solium-disable-next-line
    if (timestamp == uint40(block.timestamp)) {
      //if the index was updated in the same block, no need to perform any calculation
      return reserve.liquidityIndex;
    }

    uint256 cumulated =
      MathUtils.calculateLinearInterest(reserve.currentLiquidityRate, timestamp).rayMul(
        reserve.liquidityIndex
      );

    return cumulated;
  }

  /**
   * @dev Returns the ongoing normalized variable debt for the reserve
   * A value of 1e27 means there is no debt. As time passes, the income is accrued
   * A value of 2*1e27 means that for each unit of debt, one unit worth of interest has been accumulated
   * @param reserve The reserve object
   * @return The normalized variable debt. expressed in ray
   **/
  function getNormalizedDebt(DataTypes.ReserveData storage reserve)
    internal
    view
    returns (uint256)
  {
    uint40 timestamp = reserve.lastUpdateTimestamp;

    //solium-disable-next-line
    if (timestamp == uint40(block.timestamp)) {
      //if the index was updated in the same block, no need to perform any calculation
      return reserve.variableBorrowIndex;
    }

    uint256 cumulated =
      MathUtils.calculateCompoundedInterest(reserve.currentVariableBorrowRate, timestamp).rayMul(
        reserve.variableBorrowIndex
      );

    return cumulated;
  }