abstract contract ISignatureValidator is ISignatureValidatorConstants {
    /**
     * @dev Should return whether the signature provided is valid for the provided data
     * @param _data Arbitrary length data signed on the behalf of address(this)
     * @param _signature Signature byte array associated with _data
     *
     * MUST return the bytes4 magic value 0x20c13b0b when function passes.
     * MUST NOT modify state (using STATICCALL for solc < 0.5, view modifier for solc > 0.5)
     * MUST allow external calls
     */
    function isValidSignature(bytes memory _data, bytes memory _signature) public view virtual returns (bytes4);
}
function isValidSignature(bytes memory _data, bytes memory _signature) public view virtual returns (bytes4);

/**
 * @dev Should return whether the signature provided is valid for the provided data
 * @param _data Arbitrary length data signed on the behalf of address(this)
 * @param _signature Signature byte array associated with _data
 *
 * MUST return the bytes4 magic value 0x20c13b0b when function passes.
 * MUST NOT modify state (using STATICCALL for solc < 0.5, view modifier for solc > 0.5)
 * MUST allow external calls
 */