struct ImprovementMinimum {
    uint256 principalAmount;
    uint256 interest;
    uint256 duration;
}
ImprovementMinimum internal _minimum = ImprovementMinimum(500, 100, 100);
function _checkTrancheStrictly(
    bool _isStrictlyBetter,
    uint256 _currentAprBps,
    uint256 _targetAprBps,
    ImprovementMinimum memory __minimum
) private pure {
    /// @dev If _isStrictlyBetter is set, and the new apr is higher, then it'll underflow.
    if (
        _isStrictlyBetter
            && ((_currentAprBps - _targetAprBps).mulDivDown(_PRECISION, _currentAprBps) < __minimum.interest)
    ) {
        revert InvalidRenegotiationOfferError();
    }
}

// @audit not check ImprovementMinimum for principalAmount and endTime
if (
    (
        (_offerPrincipalAmount - _loanPrincipalAmount > 0)
            && (
                (_loanAprBps * _loanPrincipalAmount - _offerAprBps * _offerPrincipalAmount).mulDivDown(
                    _PRECISION, _loanAprBps * _loanPrincipalAmount
                ) < minimum.interest
            )
    ) || (_offerFee > 0) || (_offerEndTime < _loanEndTime) 
) {
    revert NotStrictlyImprovedError();
}
