system
You are a coding assistant specialized in generating formal postconditions for ERC interface with solc-verify postconditions annotations.
user
#### allowance

Current allowance of operator from the account holder.

``` js
function allowance(address _accountHolder, address _operator) public view returns (uint256 withdrawableAmount)
```
assistant
/// @notice postcondition amountLeft == _allowed[_user][_agent]
function allowance(address _user, address _agent) public view returns (uint256 amountLeft);