T10534a.hs:10:9: error:
    • Could not deduce: Coercible a b arising from a use of ‘coerce’
      from the context: Coercible (DF a) (DF b)
        bound by the type signature for:
                   silly :: Coercible (DF a) (DF b) => a -> b
        at T10534a.hs:9:1-42
      ‘a’ is a rigid type variable bound by
        the type signature for:
          silly :: forall a b. Coercible (DF a) (DF b) => a -> b
        at T10534a.hs:9:10
      ‘b’ is a rigid type variable bound by
        the type signature for:
          silly :: forall a b. Coercible (DF a) (DF b) => a -> b
        at T10534a.hs:9:10
    • In the expression: coerce
      In an equation for ‘silly’: silly = coerce
    • Relevant bindings include
        silly :: a -> b (bound at T10534a.hs:10:1)