bool                     operator<                        ( const CInvoice & x ) const {
      if (this->m_buyer < x.Buyer()) {
        return false;
      }
      if (this->m_buyer > x.Buyer()) {
        return true;
      }
      if (this->m_seller < x.Seller()) {
        return false;
      }
      if (this->m_seller > x.Seller()) {
        return true;
      }if (this->m_date.Compare(x.Date()) > 0) {
        return false;
      }
      if (this->m_date.Compare(x.Date()) < 0) {
        return true;
      } 
      if (this->m_amount != x.Amount()) {
        return this->m_amount < x.Amount();
      }
      if (this->m_vat != x.VAT()) {
        return this->m_vat < x.VAT();
      }
        return this->m_id < x.ID(); 
    }