contract SafeStandardToken is ERC20, SafeBasicToken
{
    /** Map address => (address => value)
    *   allowed[_owner][_spender] represents the amount of tokens the _spender can use on behalf of the _owner
    */
    mapping(address => mapping(address => uint256)) allowed;


    /** Return the allowance of the _spender on behalf of the _owner
    * @param _owner address The address which owns the funds.
    * @param _spender address The address which will be allowed to spend the funds.
    * @return A uint256 specifying the amount of tokens still available for the spender.
    */
    function allowance(address _owner, address _spender) public constant returns (uint256 remaining)
    {
        return allowed[_owner][_spender];
    }


    /** Allow the _spender to spend _value tokens on behalf of msg.sender.
     * To avoid race condition, the current allowed amount must be first set to 0 through a different transaction.
     * @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)
    {
        require(_value == 0 || allowed[msg.sender][_spender] == 0);
        allowed[msg.sender][_spender] = _value;
        Approval(msg.sender, _spender, _value);
        return true;
    }


    /** Increase the allowance for _spender by _addedValue (to be use when allowed[_spender] > 0)
     */
    function increaseApproval(address _spender, uint _addedValue) public returns (bool success)
    {
        allowed[msg.sender][_spender] = allowed[msg.sender][_spender].add(_addedValue);
        Approval(msg.sender, _spender, allowed[msg.sender][_spender]);
        return true;
    }


    /** Decrease the allowance for _spender by _subtractedValue. Set it to 0 if _subtractedValue is less then the current allowance
    */
    function decreaseApproval(address _spender, uint _subtractedValue) public returns (bool success)
    {
        uint oldValue = allowed[msg.sender][_spender];

        if (_subtractedValue > oldValue)
            allowed[msg.sender][_spender] = 0;
        else
            allowed[msg.sender][_spender] = oldValue.sub(_subtractedValue);
        Approval(msg.sender, _spender, allowed[msg.sender][_spender]);
        return true;
    }


    /** Transfer tokens on behalf of _from to _to (if allowed)
     * @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 amount of tokens to be transferred
     */
    function transferFrom(address _from, address _to, uint256 _value) public returns (bool)
    {
        require(_to != address(0));
        uint256 _allowance = allowed[_from][msg.sender];
        balances[_from] = balances[_from].sub(_value);
        balances[_to] = balances[_to].add(_value);
        allowed[_from][msg.sender] = _allowance.sub(_value);
        Transfer(_from, _to, _value);
        return true;
    }
}
/** @title Standard ERC20 token
 *
 * @dev Implementation of the basic standard token.
 * @dev https://github.com/ethereum/EIPs/issues/20
 * @dev Based on code by FirstBlood: https://github.com/Firstbloodio/token/blob/master/smart_contract/FirstBloodToken.sol
 */
function allowance(address _owner, address _spender) public constant returns (uint256 remaining)
{
    return allowed[_owner][_spender];
}

/** Return the allowance of the _spender on behalf of the _owner
 * @param _owner address The address which owns the funds.
 * @param _spender address The address which will be allowed to spend the funds.
 * @return A uint256 specifying the amount of tokens still available for the spender.
 */