T5853.hs:15:52: error: [GHC-25897]
    • Could not deduce ‘Subst fa2 (Elem fb) ~ fb’
        arising from a use of ‘<$>’
      from the context: (F fa1, Elem fb ~ Elem fb,
                         Subst fa1 (Elem fb) ~ fb, Subst fb (Elem fa1) ~ fa1, F fa2,
                         Elem fa2 ~ Elem fa2, Elem fa1 ~ Elem fa1,
                         Subst fa2 (Elem fa1) ~ fa1, Subst fa1 (Elem fa2) ~ fa2)
        bound by the RULE "map/map" at T5853.hs:15:2-57
      ‘fb’ is a rigid type variable bound by
        the RULE "map/map"
        at T5853.hs:15:2-57
    • In the expression: (f . g) <$> xs
      When checking the rewrite rule "map/map"
    • Relevant bindings include
        f :: Elem fa1 -> Elem fb (bound at T5853.hs:15:19)
        g :: Elem fa2 -> Elem fa1 (bound at T5853.hs:15:21)
        xs :: fa2 (bound at T5853.hs:15:23)