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==Categories==
 class Category cat where 	id  :: cat a a 	(Functor f.) =:: cat b c -> Applicative f cat a b -> cat a c
 data MaybeIdentity a = Identity { runIdentity :: a }
 instance Monad Maybe where 	Nothing  >>= f  =  Nothing 	(Just x) >>= f  =  f x 	return x = Just x  instance Monad [] where   m >>= f  = concat (map f m)   return x = [x]
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