code: public static Optional<GeneratorSet> reduce( SystemInputDef inputDef)
      {
      return reduce( inputDef, GeneratorSet.basicGenerator(), null, new ReducerOptions());
      }
docs: For a {@link SystemInputDef system input definition}, returns a set of {@link GeneratorSet test case generators}
  that {@link #reduce( SystemInputDef, GeneratorSet, SystemTestDef, ReducerOptions) reduces}
  the number of test cases normally generated, using default {@link ReducerOptions options}.
  Returns <CODE>Optional.empty()</CODE> if test cases were not reduced.