contract StandardToken is ERC20, BasicToken {



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





  /**

   * @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 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];



    // Check is not needed because sub(_allowance, _value) will already throw if this condition is not met

    // require (_value <= _allowance);



    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;

  }



  /**

   * @dev Approve the passed address to spend the specified amount of tokens on behalf of msg.sender.

   *

   * Beware that changing an allowance with this method brings the risk that someone may use both the old

   * and the new allowance by unfortunate transaction ordering. One possible solution to mitigate this

   * race condition is to first reduce the spender's allowance to 0 and set the desired value afterwards:

   * https://github.com/ethereum/EIPs/issues/20#issuecomment-263524729

   * @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) {

    allowed[msg.sender][_spender] = _value;

    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 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];

  }



  /**

   * approve should be called when allowed[_spender] == 0. To increment

   * allowed value is better to use this function to avoid 2 calls (and wait until

   * the first transaction is mined)

   * From MonolithDAO Token.sol

   */

  function increaseApproval (address _spender, uint _addedValue) returns (bool success) {

    allowed[msg.sender][_spender] = allowed[msg.sender][_spender].add(_addedValue);

    Approval(msg.sender, _spender, allowed[msg.sender][_spender]);

    return true;

  }



  function decreaseApproval (address _spender, uint _subtractedValue) 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;

  }

}
function allowance(address _owner, address _spender) public constant returns (uint256 remaining) {

    return allowed[_owner][_spender];

  }
/**
 
 * @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 specifying the amount of tokens still available for the spender.
 
 */