deriving-via-fail4.hs:14:12: error:
    • Couldn't match representation of type ‘Int’ with that of ‘Char’
        arising from the coercion of the method ‘==’
          from type ‘Char -> Char -> Bool’ to type ‘F1 -> F1 -> Bool’
    • When deriving the instance for (Eq F1)

deriving-via-fail4.hs:17:13: error:
    • Couldn't match representation of type ‘a’ with that of ‘a1’
        arising from the coercion of the method ‘c’
          from type ‘a -> a -> Bool’ to type ‘a -> F2 a1 -> Bool’
      ‘a’ is a rigid type variable bound by
        the deriving clause for ‘C a (F2 a1)’
        at deriving-via-fail4.hs:17:13-15
      ‘a1’ is a rigid type variable bound by
        the deriving clause for ‘C a (F2 a1)’
        at deriving-via-fail4.hs:17:13-15
    • When deriving the instance for (C a (F2 a1))