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);