contract ERC721Interface {
    // Required methods
    // function totalSupply() public view returns (uint256 total);
    // function balanceOf(address _owner) public view returns (uint256 balance);
    function ownerOf(uint256 _tokenId) external view returns (address owner);
    // function approve(address _to, uint256 _tokenId) external;
    // function transfer(address _to, uint256 _tokenId) external;
    // function transferFrom(address _from, address _to, uint256 _tokenId) external;
}
function ownerOf(uint256 _tokenId) external view returns (address owner);

// Required methods
// function totalSupply() public view returns (uint256 total);
// function balanceOf(address _owner) public view returns (uint256 balance);