code: public static Optional<ITestCaseGenerator> reduce( FunctionInputDef inputDef)
      {
      return reduce( inputDef, new TupleGenerator(), null, new ReducerOptions());
      }
docs: For a {@link FunctionInputDef function input definition}, returns a {@link ITestCaseGenerator test case generator}
  that {@link #reduce( FunctionInputDef, ITestCaseGenerator, FunctionTestDef, 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.