module Prelude where

gcd		:: (Integral a) => a -> a -> a
gcd 0 0 = error "Prelude.gcd: gcd 0 0 is undefined."
gcd x y	= gcd' (abs x) (abs y)
          where gcd' :: (Integral a) => a -> a -> a
                gcd' x 0 = x
                gcd' x y = gcd' y (x `rem` y)