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

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