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