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{-# LANGUAGE DataKinds, FunctionalDependencies, FlexibleInstances,
UndecidableInstances, PolyKinds, KindSignatures,
ConstraintKinds, FlexibleContexts #-}
module T6020 where
class Id (a :: k) (b :: k) | a -> b
instance Id a a
f :: Id x y => x -> y
f = f
--class Test (x :: a) (y :: a) | x -> y
--instance (Id x y, Id y z) => Test x z
-- (Id x0 y0, Id y0 z0, x~x0, z~z0)
-- (Id x y0, Id y0 z, y0~z, y0~y)
--test :: Test True True => ()
--test = ()
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