let true = \x y. x in
let false = \x y. y in
let and = \l r. l (r true false) false in
+let or = \l r. l true r in
+;
let make\_pair = \f s g. g f s in
let get\_fst = true in
let get\_snd = false in
let iszero = \n. n (\x. false) true in
let succ = \n s z. s (n s z) in
let mul = \m n s. m (n s) in
-let pred = \n. iszero n 0 (length (tail (n (\p. make\_list junk p) empty))) in
+let pred = (\shift n. n shift (make\_pair 0 0) get\_snd) (\p. p (\x y. make\_pair (succ x) x)) in
let leq = \m n. iszero(n pred m) in
let eq = \m n. and (leq m n)(leq n m) in
;
let isZero = iszero in
let mult = mul in
;
+let t1 = (make_list 1 empty) in
+let t2 = (make_list 2 empty) in
+let t3 = (make_list 3 empty) in
+let t12 = (make_list t1 (make_list t2 empty)) in
+let t23 = (make_list t2 (make_list t3 empty)) in
+let ta = (make_list t1 t23) in
+let tb = (make_list t12 t3) in
+let tc = (make_list t1 (make_list t23 empty)) in
+;
+;sum-leaves t1 ~~> 1
+;sum-leaves t2 ~~> 2
+;sum-leaves t3 ~~> 3
+;sum-leaves t12 ~~> 3
+;sum-leaves t23 ~~> 5
+;sum-leaves ta ~~> 6
+;sum-leaves tb ~~> 6
+;
length (tail mylist)
</textarea>