Withdraw underlying asset

withdraw is used in withdrawing an underlying asset from the protocol

function withdraw(
        MarketParams memory marketParams,
        uint256 assets,
        uint256 shares,
        address onBehalf,
        address receiver
    ) external returns (uint256, uint256) {
        Id id = marketParams.id();
        require(market[id].lastUpdate != 0, ErrorsLib.MARKET_NOT_CREATED);
        require(UtilsLib.exactlyOneZero(assets, shares), ErrorsLib.INCONSISTENT_INPUT);
        require(receiver != address(0), ErrorsLib.ZERO_ADDRESS);
        // No need to verify that onBehalf != address(0) thanks to the following authorization check.
        require(_isSenderAuthorized(onBehalf), ErrorsLib.UNAUTHORIZED);

        _accrueInterest(marketParams, id);

        if (assets > 0) shares = assets.toSharesUp(market[id].totalSupplyAssets, market[id].totalSupplyShares);
        else assets = shares.toAssetsDown(market[id].totalSupplyAssets, market[id].totalSupplyShares);

        position[id][onBehalf].supplyShares -= shares;
        market[id].totalSupplyShares -= shares.toUint128();
        market[id].totalSupplyAssets -= assets.toUint128();

        require(market[id].totalBorrowAssets <= market[id].totalSupplyAssets, ErrorsLib.INSUFFICIENT_LIQUIDITY);

        emit EventsLib.Withdraw(id, msg.sender, onBehalf, receiver, assets, shares);

        IERC20(marketParams.loanToken).safeTransfer(receiver, assets);

        return (assets, shares);
    }