I want to write a function that, given a non-negative integer n, returns the power set of {1,...,n}. So I want to use the Set.S module as found [here](http://caml.inria.fr/pub/docs/manual-ocaml/libref/Set.S.html). But I can't seem to import it. When I run the following code:

```
open Set.S

let rec power_set n =
  if n = 0 then add empty empty else union (iter (add n s) power_set (n-1)) (power_set (n-1));;

let print_set s = SS.iter print_endline s;;

print_set (power_set 2)

```

I get the error:

```
File "countTopologies.ml", line 1, characters 5-10:
Error: Unbound module Set.S

```

Maybe I just don't have the Set.S module installed on my computer? (I've only done the bare bones needed to install OCaml). If this is the case, how would I get it?