void Inventory::receive(Product newp)
{
   cout << "Received Shipment of product "
      << newp << "\n";
   list<int>::iterator we_need =
      find(on_order.begin(), on_order.end(), newp.get_id());
   if (we_need != on_order.end())
   {
      cout << "Ship " << newp
         << " to fill back order\n";
      on_order.erase(we_need);
   }
   else
      on_hand.push_front(newp);
}