sbool contains(Collection c, O o) {
  ret c != null && c.contains(o);
}

sbool <A> contains(Iterable<A> it, A a) {
  if (it != null)
    while (it.hasNext())
      if (eq(a, it.next()))
        true;
  false;
}

static bool contains(O[] x, O o) {
  if (x != null)
    for (O a : x)
      if (eq(a, o))
        true;
  false;
}

static bool contains(S s, char c) {
  ret s != null && s.indexOf(c) >= 0;
}

static bool contains(S s, S b) {
  ret s != null && s.indexOf(b) >= 0;
}

static bool contains(BitSet bs, int i) {
  ret bs != null && bs.get(i);
}

ifclass Producer
static <A> bool contains(Producer<A> p, A a) {
  if (p != null && a != null) while true {
    A x = p.next();
    if (x == null) break;
    if (eq(x, a)) true;
  }
  false;
}
endif