T5853.stderr 825 Bytes
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T5853.hs:15:46: error:
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    • Could not deduce: Subst (Subst fa a) b ~ Subst fa b
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        arising from a use of ‘<$>’
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      from the context: (F fa, Elem (Subst fa b) ~ b,
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                         Subst fa b ~ Subst fa b, Subst (Subst fa b) (Elem fa) ~ fa,
                         F (Subst fa a), Elem (Subst fa a) ~ a, Elem fa ~ Elem fa,
                         Subst (Subst fa a) (Elem fa) ~ fa, Subst fa a ~ Subst fa a)
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        bound by the RULE "map/map" at T5853.hs:15:2-57
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      NB: ‘Subst’ is a non-injective type family
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    • In the expression: (f . g) <$> xs
      When checking the transformation rule "map/map"
    • Relevant bindings include
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        f :: Elem fa -> b (bound at T5853.hs:15:19)
        g :: a -> Elem fa (bound at T5853.hs:15:21)
        xs :: Subst fa a (bound at T5853.hs:15:23)