six.lc

let true = lambda t f. t in
let false = lambda t f. f in
let and = lambda b1 b2. b1 b2 false in
let or = lambda b1 b2. b1 true b2 in
let not = lambda b. b false true in

let zero = lambda s z. z in
let succ = lambda n. lambda s z. s (n s z) in

let one = succ zero in
let two = succ one in
let three = succ two in
let four = succ three in
let five = succ four in

let plus = lambda m n. m succ n in
let times = lambda m n. m (plus n) zero in
let iszero = lambda n. n (lambda x. false) true in

let pair = lambda a b. lambda c. c a b in
let fst = lambda p. p (lambda a b. a) in
let snd = lambda p. p (lambda a b. b) in

let pred = lambda n. snd (n (lambda p. pair (succ (fst p)) (fst p))
(pair zero zero)) in
let sub = lambda m n. n pred m in

let equal = lambda m n. and (iszero (sub m n)) (iszero (sub n m)) in

let Y = lambda f. (lambda x. f (x x)) (lambda x y. f (x x) y) in
let fact = Y (lambda f n. (iszero n) (lambda x. succ zero) (lambda x.
times n (f (pred n))) (lambda x. x)) in

let ten = times two five in
let twelve = times three four in
let onetwenty = times ten twelve in

(and (equal (fact three) (succ five)) (equal (fact five) onetwenty)) one
zero