contract ERC721 {
    // Events
    event Transfer(address indexed _from, address indexed _to, uint256 _tokenId);
    event Approval(address indexed _owner, address indexed _approved, uint256 _tokenId);

    /// For querying totalSupply of token.
    function totalSupply() public view returns (uint256 _totalSupply);

    /// For querying balance of a particular account.
    /// @param _owner The address for balance query.
    /// @dev Required for ERC-721 compliance.
    function balanceOf(address _owner) public view returns (uint256 _balance);

    /// For querying owner of token.
    /// @param _tokenId The tokenID for owner inquiry.
    /// @dev Required for ERC-721 compliance.
    function ownerOf(uint256 _tokenId) public view returns (address _owner);

    /// @notice Grant another address the right to transfer token via takeOwnership() and transferFrom()
    /// @param _to The address to be granted transfer approval. Pass address(0) to
    ///  clear all approvals.
    /// @param _tokenId The ID of the Token that can be transferred if this call succeeds.
    /// @dev Required for ERC-721 compliance.
    function approve(address _to, uint256 _tokenId) public;

    // NOT IMPLEMENTED
    // function getApproved(uint256 _tokenId) public view returns (address _approved);

    /// Third-party initiates transfer of token from address _from to address _to.
    /// @param _from The address for the token to be transferred from.
    /// @param _to The address for the token to be transferred to.
    /// @param _tokenId The ID of the Token that can be transferred if this call succeeds.
    /// @dev Required for ERC-721 compliance.
    function transferFrom(address _from, address _to, uint256 _tokenId) public;

    /// Owner initates the transfer of the token to another account.
    /// @param _to The address of the recipient, can be a user or contract.
    /// @param _tokenId The ID of the token to transfer.
    /// @dev Required for ERC-721 compliance.
    function transfer(address _to, uint256 _tokenId) public;

    ///
    function implementsERC721() public view returns (bool _implementsERC721);

    // EXTRA
    /// @notice Allow pre-approved user to take ownership of a token.
    /// @param _tokenId The ID of the token that can be transferred if this call succeeds.
    /// @dev Required for ERC-721 compliance.
    function takeOwnership(uint256 _tokenId) public;
}
/**
 * Interface for required functionality in the ERC721 standard
 * for non-fungible tokens.
 *
 * Author: Nadav Hollander (nadav at dharma.io)
 * https://github.com/dharmaprotocol/NonFungibleToken/blob/master/contracts/ERC721.sol
 */
function takeOwnership(uint256 _tokenId) public;

/// @notice Allow pre-approved user to take ownership of a token.
/// @param _tokenId The ID of the token that can be transferred if this call succeeds.
/// @dev Required for ERC-721 compliance.