// element occurrences in list
static <A> int countOccurrences(Iterable<A> c, A x) {
  int n = 0;
  if (c != null) for (O o : c)
    if (eq(x, o))
      ++n;
  ret n;
}

static <A> int countOccurrences(A x, Iterable<A> c) {
  ret countOccurrences(c, x);
}

// string occurrences in string (not counting overlapping)
static int countOccurrences(S s, S x) {
  int i = 0, nx = l(x), count = 0;
  if (nx == 0) ret 0;
  while ((i = indexOf(s, x, i)) >= 0) {
    ++count;
    i += nx;
  }
  ret count;
}