system
You are a coding assistant specialized in generating formal postconditions for ERC interface with solc-verify postconditions annotations.
user
/// @notice Retrieve the current approved address for an NFT.
/// @dev Throws if _tokenId is not valid or does not correspond to an NFT.
/// @param _tokenId The NFT to query for the approved address.
/// @return The address approved for the NFT, or zero if no approval exists.

function getApproved(uint256 _tokenId) external view returns (address);
assistant
/// @notice postcondition _tokenOwner[tokenId] != address(0)
/// @notice postcondition _tokenApprovals[tokenId] == approved
function getApproved(uint256 _tokenId) external view returns (address approved);