[Haskell-cafe] On to applicative

I'm looking at a discussion of Either (as functor) here: http://learnyouahaskell.com/making-our-own-types-and-typeclasses#the-functor... instance Functor (Either a) where       fmap f (Right x) = Right (f x)       fmap f (Left x) = Left x And this line in Data.Either Functor (Either a) but no fmap defined here. How come? Michael