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{-# LANGUAGE TypeFamilies, FlexibleContexts, UndecidableInstances #-}
module Main where
newtype Mu f = Mu (f (Mu f))
type family Id m
type instance Id m = m
instance Show (Id (f (Mu f))) => Show (Mu f) where
show (Mu f) = show f
showMu :: Mu (Either ()) -> String
showMu = show
item :: Mu (Either ())
item = Mu (Right (Mu (Left ())))
main = print (showMu item)
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