let rec

   EltMember = lambda x. lambda L.
     if      null L   then false
     else if x = hd L then true
     else EltMember x tl L,

   ListEq = lambda x. lambda y.
      if      null x      then null y
      else if null y      then false
      else if hd x = hd y then ListEq tl x tl y
      else false,

   ListMember = lambda L. lambda LL.
     if      null LL          then false
        else if ListEq L (hd LL) then true
     else ListMember L tl LL,

   Combinatorial = lambda Length.
     if Length = 0 then (nil :: nil)
     else list L st   EltMember (hd L) (1::(2::nil)) and
                     ListMember (tl L) (Combinatorial (Length-1))

in Combinatorial 2