code: @Override
      public boolean contains(IAtom atom) {
          if (focus.equals(atom) || (focus instanceof IBond && ((IBond) focus).contains(atom)))
              return true;
          for (C carrier : carriers) {
              if (carrier.equals(atom) ||
                  (carrier instanceof IBond && ((IBond) carrier).contains(atom)))
                  return true;
          }
          return false;
      }
docs: {@inheritDoc}