{-# LANGUAGE FlexibleInstances #-}
-- This doesn't work: GHC MUST pick the wrong one!
-- {-# LANGUAGE IncoherentInstances #-}
unit p where
    signature A where
        data K a
        instance Show a => Show (K a)
unit q where
    signature A where
        data K a
        instance Read a => Show (K a)
unit r where
    dependency p[A=<A>]
    dependency q[A=<A>]
    module R where
        import A
        f :: Show a => K a -> String
        f = show
        g :: Read a => K a -> String
        g = show