svoid stepAllWithStats_multiThreaded(Steppable s) {
  if (s cast SplittableSteppable) {
    int cores = coresToUse();
    if (cores > 1) {
      long n = 0;
      final MultiThreadStepper stepper = new(s.split(cores));
      final new Flag done;
      stepper.onDone(r {
        print(n2(stepper.steps(), "step") + " in " + stepper.elapsedTime + " ms");
        done.raise();
      });
      done.waitUntilUp();
      ret;
    }
  }
  stepAllWithStats(s);
}