contract ERC165 is IERC165 {
	/*
 	* bytes4(keccak256('supportsInterface(bytes4)')) == 0x01ffc9a7
 	*/
	bytes4 private constant _INTERFACE_ID_ERC165 = 0x01ffc9a7;

	/**
 	* @dev Mapping of interface ids to whether or not it's supported.
 	*/
	mapping(bytes4 => bool) private _supportedInterfaces;

	constructor () internal {
    	// Derived contracts need only register support for their own interfaces,
    	// we register support for ERC165 itself here
    	_registerInterface(_INTERFACE_ID_ERC165);
	}

	/**
 	* @dev See {IERC165-supportsInterface}.
 	*
 	* Time complexity O(1), guaranteed to always use less than 30 000 gas.
 	*/
	function supportsInterface(bytes4 interfaceId) external view returns (bool) {
    	return _supportedInterfaces[interfaceId];
	}

	/**
 	* @dev Registers the contract as an implementer of the interface defined by
 	* `interfaceId`. Support of the actual ERC165 interface is automatic and
 	* registering its interface id is not required.
 	*
 	* See {IERC165-supportsInterface}.
 	*
 	* Requirements:
 	*
 	* - `interfaceId` cannot be the ERC165 invalid interface (`0xffffffff`).
 	*/
	function _registerInterface(bytes4 interfaceId) internal {
    	require(interfaceId != 0xffffffff, "ERC165: invalid interface id");
    	_supportedInterfaces[interfaceId] = true;
	}
}
/**
 * @dev Implementation of the {IERC165} interface.
 *
 * Contracts may inherit from this and call {_registerInterface} to declare
 * their support of an interface.
 */
function _registerInterface(bytes4 interfaceId) internal {
   	require(interfaceId != 0xffffffff, "ERC165: invalid interface id");
   	_supportedInterfaces[interfaceId] = true;
}

/**
 	* @dev Registers the contract as an implementer of the interface defined by
 	* `interfaceId`. Support of the actual ERC165 interface is automatic and
 	* registering its interface id is not required.
 	*
 	* See {IERC165-supportsInterface}.
 	*
 	* Requirements:
 	*
 	* - `interfaceId` cannot be the ERC165 invalid interface (`0xffffffff`).
 	*/