T14066d.hs:11:35: error:
    • Couldn't match type ‘b1’ with ‘b’
      ‘b1’ is a rigid type variable bound by
        a type expected by the context:
          forall c b1 (a :: c). (Proxy a, Proxy c, b1)
        at T14066d.hs:11:35
      ‘b’ is a rigid type variable bound by
        the type signature for:
          f :: forall b. b -> (Proxy Maybe, ())
        at T14066d.hs:10:1-37
      Expected type: (Proxy a, Proxy c, b1)
        Actual type: (Proxy a, Proxy c, b)
    • In the first argument of ‘g’, namely ‘y’
      In the expression: g y
      In the expression: (fstOf3 y :: Proxy Maybe, g y)
    • Relevant bindings include
        y :: forall k1 k2 (a :: k1) (c :: k2). (Proxy a, Proxy c, b)
          (bound at T14066d.hs:15:5)
        x :: b (bound at T14066d.hs:11:3)
        f :: b -> (Proxy Maybe, ()) (bound at T14066d.hs:11:1)