function pay(PayParam calldata param)
    external 
    override 
    lock 
    returns (
        uint128 assetIn, 
        uint128 collateralOut
    ) 
{
    require(block.timestamp < param.maturity, 'E202');
    require(param.owner != address(0), 'E201');
    require(param.to != address(0), 'E201');
    require(param.to != address(this), 'E204');
    require(param.ids.length == param.assetsIn.length, 'E205');
    require(param.ids.length == param.collateralsOut.length, 'E205');

    Pool storage pool = pools[param.maturity];

    Due[] storage dues = pool.dues[param.owner];
    require(dues.length >= param.ids.length, 'E205');

    for (uint256 i; i < param.ids.length;) {
        Due storage due = dues[param.ids[i]];
        require(due.startBlock != BlockNumber.get(), 'E207');
        if (param.owner != msg.sender) require(param.collateralsOut[i] == 0, 'E213');
        require(uint256(assetIn) * due.collateral >= uint256(collateralOut) * due.debt, 'E303');
        due.debt -= param.assetsIn[i];
        due.collateral -= param.collateralsOut[i];
        assetIn += param.assetsIn[i];
        collateralOut += param.collateralsOut[i];
        unchecked { ++i; }
    }
    ...
for (uint256 i; i < param.ids.length;) {
    Due storage due = dues[param.ids[i]];
    require(due.startBlock != BlockNumber.get(), 'E207');
    if (param.owner != msg.sender) require(param.collateralsOut[i] == 0, 'E213');
    due.debt -= param.assetsIn[i];
    due.collateral -= param.collateralsOut[i];
    assetIn += param.assetsIn[i];
    collateralOut += param.collateralsOut[i];
    unchecked { ++i; }
}

require(uint256(assetIn) * due.collateral >= uint256(collateralOut) * due.debt, 'E303');
...
