function withdraw (uint256 _value)
  returns (bool _success) {
    if (msg.sender != client) throw;

    if (_value > 0) {
      updateCapital ();
      if (_value <= capital) {
        if (client.send (_value)) {
          Withdrawal (_value);
          capital -= _value;
          return true;
        } else return false;
      } else return false;
    } else return true;
  }