interface ERC721TokenReceiver
{
    /// @notice Handle the receipt of an NFT
    /// @dev The ERC721 smart contract calls this function on the
    /// recipient after a `transfer`. This function MAY throw to revert and reject the transfer. Return
    /// of other than the magic value MUST result in the transaction being reverted.
    /// @notice 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 transferred
    /// @param _data Additional data with no specified format
    /// @return `bytes4(keccak256("onERC721Received(address,address,uint256,bytes)"))`
    /// unless throwing
    function onERC721Received(address _operator, address _from, uint256 _tokenId, bytes calldata _data) external returns(bytes4);
}
function onERC721Received(address _operator, address _from, uint256 _tokenId, bytes calldata _data) external returns(bytes4);
/// @notice Handle the receipt of an NFT
/// @dev The ERC721 smart contract calls this function on the
/// recipient after a `transfer`. This function MAY throw to revert and reject the transfer. Return
/// of other than the magic value MUST result in the transaction being reverted.
/// @notice 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 transferred
/// @param _data Additional data with no specified format
/// @return `bytes4(keccak256("onERC721Received(address,address,uint256,bytes)"))`
/// unless throwing