contract ERC721 {
  // Required:
    function approve(address to, uint256 tokenId) public; 
    function balanceOf(address owner) public view returns (uint256 balance);
    function implementsERC721() public pure returns (bool);
    function ownerOf(uint256 tokenId) public view returns (address addr);
    function takeOwnership(uint256 tokenId) public;
    function totalSupply() public view returns (uint256 total);
    function transferFrom(address from, address to, uint256 tokenId) public;
    function transfer(address to, uint256 tokenId) public;

    event Transfer(address indexed from, address indexed to, uint256 tokenId);
    event Approval(address indexed owner, address indexed approved, uint256 indexed tokenId);

    /** ERC721Metadata */ 
    function name() external view returns (string name);
    function symbol() external view returns (string symbol);
    function tokenURI(uint256 _tokenId) external view returns (string uri); 
  }
/**
 * @title ERC721 Non-Fungible Token Standard basic interface
 * @dev see https://github.com/ethereum/EIPs/blob/master/EIPS/eip-721.md
 */
function approve(address to, uint256 tokenId) public;
// Required: