contract Petrifiable is Initializable {
    // Use block UINT256_MAX (which should be never) as the initializable date
    uint256 internal constant PETRIFIED_BLOCK = uint256(-1);

    function isPetrified() public view returns (bool) {
        return getInitializationBlock() == PETRIFIED_BLOCK;
    }

    /**
    * @dev Function to be called by top level contract to prevent being initialized.
    *      Useful for freezing base contracts when they're used behind proxies.
    */
    function petrify() internal onlyInit {
        initializedAt(PETRIFIED_BLOCK);
    }
}
function petrify() internal onlyInit {
    initializedAt(PETRIFIED_BLOCK);
}

/**
 * @dev Function to be called by top level contract to prevent being initialized.
 *      Useful for freezing base contracts when they're used behind proxies.
 */