code: public boolean isDownOptional() {
          int i;
          int max;
          Alternative ab;
  
          max = alternatives.size();
          for (i = 0; i < max; i++) {
              ab = alternatives.get(i);
              if (ab.getArgCount() == 0) {
                  return true;
              }
          }
          return false;
      }
docs: Is down optional.
  pre:   this is kind of reduced (e.g. results from createReduced