abstract contract DateTimeAPI {
    /*
     *  Abstract contract for interfacing with the DateTime contract.
     *
     */
    function isLeapYear(uint16 year) public pure virtual returns (bool);

    function toTimestamp(
        uint16 year,
        uint8 month,
        uint8 day
    ) public pure virtual returns (uint256 timestamp);

    function toTimestamp(
        uint16 year,
        uint8 month,
        uint8 day,
        uint8 hour,
        uint8 minute,
        uint8 second
    ) public pure virtual returns (uint256 timestamp);
}
function isLeapYear(uint16 year) public pure virtual returns (bool);

/*
 *  Abstract contract for interfacing with the DateTime contract.
 *
 */