{-# RULES
"fold/build" forall k z (g :: forall b. (a -> b -> b) -> b -> b). foldr k z (build g) = g k z
  #-}

{-# RULES
"fold/build"
  forall k z
         (g :: forall b.
           (a -> b -> b) -> b -> b).
              foldr k z (build g) =
              g k z
  #-}