static <A> bool containsAny(Collection<A> a, Collection<A> b) {
  if (empty(a)) false;
  Set<A> set = asSet(b);
  for (A x : a)
    if (contains(set, x))
      true;
  false;
}

static <A> bool containsAny(Map<A, B> a, Collection<A> b) {
  if (empty(a)) false;
  Set<A> set = asSet(b);
  for (A x : a)
    if (a.containsKey(x))
      true;
  false;
}