∀ {α : Type u_1} {β : Type u_2} {γ : Type u_3} {δ : Type u_4} {as : Array α} {bs : Array β} {g : δ → γ → δ}
  {f : α → β → γ} {i : δ},
  Array.foldl g i (Array.zipWith f as bs) = Array.foldl (fun r p => g r (f p.1 p.2)) i (as.zip bs)