Church numerals mult m n s z = m (n s) z

gistfile1.hs

zero s z = z
succ n s z = s (n s z)
one s z = s z
two s z = s (s z)

false x y = y = zero x y 
true  x y = x = const x y

const x y = x

isZero n = n (const false) true

mult m n s z = m (n s) z
             = (m . n) s z


-- http://stackoverflow.com/questions/12942397/
-- lambda-calculus-in-haskell-is-there-some-way-to-make-
-- church-numerals-type-check/12942637#12942637