contract StandardToken is ERC20 {
    using SafeMath for uint256;
    mapping (address => mapping (address => uint256)) allowed;
    mapping(address => uint256) balances;

    /**
     * @dev transfer token for a specified address
     * @param _to The address to transfer to.
     * @param _value The amount to be transferred.
     */
    function transfer(address _to, uint256 _value) public returns (bool){
        // require(0 < _value); -- REMOVED AS REQUESTED BY AUDIT
        require(balances[msg.sender] >= _value);
        balances[msg.sender] = balances[msg.sender].sub(_value);
        balances[_to] = balances[_to].add(_value);
        emit Transfer(msg.sender, _to, _value);
        return true;
    }

    /**
     * @dev Gets the balance of the specified address.
     * @param _owner The address to query the balance of. 
     * @return An uint256 representing the amount owned by the passed address.
     */
    function balanceOf(address _owner) view public returns (uint256 balance){
        return balances[_owner];
    }

    /**
     * @dev Transfer tokens from one address to another
     * @param _from address The address which you want to send tokens from
     * @param _to address The address which you want to transfer to
     * @param _value uint256 the amout of tokens to be transfered
     */
    function transferFrom(address _from, address _to, uint256 _value) public returns (bool){
        uint256 _allowance = allowed[_from][msg.sender];
        require (balances[_from] >= _value);
        require (_allowance >= _value);
        // require (_value > 0); // NOTE: Removed due to audit demand (transfer of 0 should be authorized)
        // require ( balances[_to] + _value > balances[_to]);
        // Check is not needed because sub(_allowance, _value) will already throw if this condition is not met
        // require (_value <= _allowance);
        balances[_to] = balances[_to].add(_value);
        balances[_from] = balances[_from].sub(_value);
        allowed[_from][msg.sender] = _allowance.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.
     * @param _spender The address which will spend the funds.
     * @param _value The amount of tokens to be spent.
     */
    function approve(address _spender, uint256 _value) public returns (bool){
        // To change the approve amount you first have to reduce the addresses`
        // allowance to zero by calling `approve(_spender, 0)` if it is not
        // already 0 to mitigate the race condition described here:
        // https://github.com/ethereum/EIPs/issues/20#issuecomment-263524729
        require((_value == 0) || (allowed[msg.sender][_spender] == 0));
        allowed[msg.sender][_spender] = _value;
        emit Approval(msg.sender, _spender, _value);
        return true;
    }

    /**
     * @dev Function to check the amount of tokens that an owner allowed to a spender.
     * @param _owner address The address which owns the funds.
     * @param _spender address The address which will spend the funds.
     * @return A uint256 specifing the amount of tokens still available for the spender.
     */
    function allowance(address _owner, address _spender) view public returns (uint256 remaining){
        return allowed[_owner][_spender];
    }
}
function balanceOf(address _owner) view public returns (uint256 balance){
    return balances[_owner];
}

/**
 * @dev Gets the balance of the specified address.
 * @param _owner The address to query the balance of. 
 * @return An uint256 representing the amount owned by the passed address.
 */