fun even i = (i mod 2) = 0;

fun odd i = not(even i);

fun upto 0 = []
   |upto n = (upto (n-1))@[n];

fun pairs e [] = []
   |pairs e (h::t) = (e,h)::(pairs e t);

fun cp [] y = []
   |cp (e::x) y = (pairs e y)@(cp x y);

(* Alternatively *)

fun cp1 x y = collapse (mapf (map pairs x) y);

(* Alternatively, using "iteration" *)

fun do_while test body s =
    if test s
    then do_while test body (body s)
    else s;

fun do_j (result,i,[]) = (result,i,[])
   |do_j (result,i,(j::js)) = (result@[(i,j)],i,js);

fun test_j (_,_,js) = not (null js);

fun do_i (result,[],js) = (result,[],js)
   |do_i (result,(i::is),js) =
          let val (new,_,_) = do_while test_j do_j (result,i,js)
          in (new,is,js) end;

fun test_i (_,is,_) = not (null is);

fun cp2 x y = let val (result,_,_) = do_while test_i do_i ([],x,y)
              in result end;