library SafeMathMod {// Partial SafeMath Library

    function sub(uint256 a, uint256 b) internal pure returns (uint256 c) {
        require((c = a - b) < a);
    }

    function add(uint256 a, uint256 b) internal pure returns (uint256 c) {
        require((c = a + b) > a);
    }
}
function sub(uint256 a, uint256 b) internal pure returns (uint256 c) {
        require((c = a - b) < a);
    }
// Partial SafeMath Library