+ let singleton = \x f z. f x z in
+ ; append list2 to list1 with: list1 make_list list2
+ let reverse = \lst. lst (\h sofar. sofar make_list (singleton h)) empty in
+ ; zip [a;b;c] [x; y; z] ~~> [(a,x);(b,y);(c,z)]
+ let zip = \left right. (\base build. reverse left build base (\x y. reverse x))
+ ; where base is
+ (make_pair empty (map (\h u. u h) right))
+ ; and build is
+ (\h sofar. sofar (\x y. isempty y
+ sofar
+ (make_pair (make_list (\u. head y (u h)) x) (tail y))
+ )) in
+ let all = \f lst. lst (\h sofar. and sofar (f h)) true in
+ let any = \f lst. lst (\h sofar. or sofar (f h)) false in
+