docs: protected static void removeProvidedDownServices(Protocol protocol, List<Integer> events) {
          if(protocol == null || events == null)
              return;
          for(Protocol prot=protocol.getUpProtocol(); prot != null && !events.isEmpty(); prot=prot.getUpProtocol()) {
              List<Integer> provided_down_services=prot.providedDownServices();
              if(provided_down_services != null && !provided_down_services.isEmpty())
                  events.removeAll(provided_down_services);
          }
      }