contract ERC721Receiver {
	  /**
	   * @dev Magic value to be returned upon successful reception of an NFT
	   *  Equals to `bytes4(keccak256("onERC721Received(address,address,uint256,bytes)"))`,
	   *  which can be also obtained as `ERC721Receiver(0).onERC721Received.selector`
	   */
	  bytes4 internal constant ERC721_RECEIVED = 0x150b7a02;

	  /**
	   * @notice Handle the receipt of an NFT
	   * @dev The ERC721 smart contract calls this function on the recipient
	   * after a `safetransfer`. This function MAY throw to revert and reject the
	   * transfer. Return of other than the magic value MUST result in the 
	   * transaction being reverted.
	   * Note: the contract address is always the message sender.
	   * @param _operator The address which called `safeTransferFrom` function
	   * @param _from The address which previously owned the token
	   * @param _tokenId The NFT identifier which is being transfered
	   * @param _data Additional data with no specified format
	   * @return `bytes4(keccak256("onERC721Received(address,address,uint256,bytes)"))`
	   */
	  function onERC721Received(
		address _operator,
		address _from,
		uint256 _tokenId,
		bytes _data
	  )
		public
		returns(bytes4);
	}
/**
 	 * @title ERC721 token receiver interface
 	 * @dev Interface for any contract that wants to support safeTransfers
 	 * from ERC721 asset contracts.
 	 */
function onERC721Received(
		address _operator,
		address _from,
		uint256 _tokenId,
		bytes _data
	  )
		public
		returns(bytes4);
/**
 	   * @notice Handle the receipt of an NFT
 	   * @dev The ERC721 smart contract calls this function on the recipient
 	   * after a `safetransfer`. This function MAY throw to revert and reject the
 	   * transfer. Return of other than the magic value MUST result in the 
 	   * transaction being reverted.
 	   * Note: the contract address is always the message sender.
 	   * @param _operator The address which called `safeTransferFrom` function
 	   * @param _from The address which previously owned the token
 	   * @param _tokenId The NFT identifier which is being transfered
 	   * @param _data Additional data with no specified format
 	   * @return `bytes4(keccak256("onERC721Received(address,address,uint256,bytes)"))`
 	   */