static Steppable combineSteppables_dontDropEnded(Iterable<? extends Steppable> steppables) {
  L<? extends Steppable> steppablesList = nonNulls(steppables);
  
  ret -> {
    bool change;
    for (s : steppablesList)
      change |= s.step();
    ret change;
  };
}

static <A extends Steppable> Steppable combineSteppables_dontDropEnded(A... steppables) {
  ret combineSteppables(asList(steppables));
}