static <A> A oneOf(L<A> l) {
  if (empty(l)) null;
  int n = l.size();
  ret n == 1 ? first(l) : l.get(defaultRandomizer().nextInt(n));
}

static char oneOf(S s) {
  ret empty(s) ? '?' : s.charAt(random(l(s)));
}

static <A> A oneOf(A... l) {
  ret oneOf(asList(l));
}