∀ {α β : Type w} {m : Type w → Type w'} {it : Std.IterM m β} [inst : Monad m] [LawfulMonad m]
  [inst_2 : Std.Iterator α m β] [Std.Iterators.Finite α m] {acc : Array β},
  Std.IterM.toArray.go it acc = (fun x => acc ++ x) <$> it.toArray