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

Transfers `_value` amount of tokens from address `_from` to address `_to`, and MUST fire the `Transfer` event.

The `transferFrom` method is used for a withdraw workflow, allowing contracts to transfer tokens on your behalf.
This can be used for example to allow a contract to transfer tokens on your behalf and/or to charge fees in sub-currencies.
The function SHOULD `throw` unless the `_from` account has deliberately authorized the sender of the message via some mechanism.

*Note* Transfers of 0 values MUST be treated as normal transfers and fire the `Transfer` event.

``` js
function transferFrom(address _from, address _to, uint256 _value) public returns (bool success)
```
assistant
/// @notice postcondition (_balances[_spender] == __verifier_old_uint(_balances[_spender]) || ( __verifier_old_uint(_balances[_spender] ==  _balances[_spender] ) - _valueAmount && _spender != _beneficiary ) && _spender == _beneficiary)
/// @notice postcondition ( _balances[_beneficiary] == __verifier_old_uint(_balances[_beneficiary]) + _valueAmount && _spender != _beneficiary ) || (_balances[_beneficiary] == __verifier_old_uint(_balances[_beneficiary]) && _spender == _beneficiary)
/// @notice postcondition __verifier_old_uint(_allowed[_spender][msg.sender]) - _valueAmount == _allowed[_spender][msg.sender]
function transferFrom(address _spender, address _beneficiary, uint256 _valueAmount) public returns (bool s)