contract StandardToken is ERC20, BasicToken {
    uint public constant MAX_UINT = 2**256 - 1;

    mapping (address => mapping (address => uint256)) internal allowed;

    /**
     */
    function transferFrom(address _from, address _to, uint256 _value) public returns (bool) {
        if (_to == address(0)) {
            totalSupply_ = totalSupply_.sub(_value);
        }

        require(_value <= balances[_from]);
        require(_value <= allowed[_from][msg.sender]);
        balances[_from] = balances[_from].sub(_value);
        balances[_to] = balances[_to].add(_value);

        /// an allowance of MAX_UINT represents an unlimited allowance.
        /// @dev see https://github.com/ethereum/EIPs/issues/717
        if (allowed[_from][msg.sender] < MAX_UINT) {
            allowed[_from][msg.sender] = allowed[_from][msg.sender].sub(_value);
        }
        emit Transfer(_from, _to, _value);
        return true;
    }
    /**
     * @dev Approve the passed address to spend the specified amount of tokens on behalf of msg.sender.
     */
    function approve(address _spender, uint256 _value) public returns (bool) {
        allowed[msg.sender][_spender] = _value;
        emit Approval(msg.sender, _spender, _value);
        return true;
    }
    /**
     */
    function allowance(address _owner, address _spender) public view returns (uint256) {
        return allowed[_owner][_spender];
    }
    /**
     * @dev Increase the amount of tokens that an owner allowed to a spender.
     */
    function increaseApproval(address _spender, uint _addedValue) public returns (bool) {
        allowed[msg.sender][_spender] = allowed[msg.sender][_spender].add(_addedValue);
        emit Approval(msg.sender, _spender, allowed[msg.sender][_spender]);
        return true;
    }
    /**
     * @dev Decrease the amount of tokens that an owner allowed to a spender.
     */
    function decreaseApproval(address _spender, uint _subtractedValue) public returns (bool) {
        uint oldValue = allowed[msg.sender][_spender];
        if (_subtractedValue > oldValue) {
            allowed[msg.sender][_spender] = 0;
        } else {
            allowed[msg.sender][_spender] = oldValue.sub(_subtractedValue);
        }
        emit Approval(msg.sender, _spender, allowed[msg.sender][_spender]);
        return true;
    }
}
/**
 * @title Standard ERC20 token
 *
 */
function allowance(address _owner, address _spender) public view returns (uint256) {
    return allowed[_owner][_spender];
}

/**
 */