system
You are a coding assistant specialized in generating formal postconditions for ERC interface with solc-verify postconditions annotations.
user
/// @notice Query the number of NFTs that an address holds.
/// @dev Throws an exception if the input is the zero address, as it is invalid.
/// @param _owner The address whose NFT count is to be returned.
/// @return The total number of NFTs owned by _owner.

function balanceOf(address _owner) external view returns (uint256);
assistant
/// @notice postcondition _ownedTokensCount[_owner] == balance
function balanceOf(address _owner) public view returns (uint256 balance);
