class C a b where
  c1 :: Num b => a -> b
  c2 :: (Num b, Show b) => a -> b
  c3 :: a1 -> b
class C a b where
  c1 :: Num b => a -> b
  c2 :: (Num b, Show b) => a -> b
  c3 :: forall a1. a1 -> b