static <A> bool containsAll(Collection<? extends A> a, Collection<A> b) {
  for (A o : b)
    if (!a.contains(o))
      false;
  true;
}

static <A> bool containsAll(Collection<? extends A> a, A... b) {
  for (A o : b)
    if (!a.contains(o))
      false;
  true;
}

sbool containsAll(S a, S... b) {
  fOr (S o : b)
    if (!contains(a, o))
      false;
  true;
}

Began life as a copy of #1001927