{α : Type w} →
  {m : Type w → Type w'} →
    {β : Type w} →
      [inst : Std.Iterator α m β] →
        {motive : Std.IteratorAccess α m → Sort u} →
          ((nextAtIdx? :
                (it : Std.IterM m β) → (n : ℕ) → m (Std.PlausibleIterStep (Std.IterM.IsPlausibleNthOutputStep n it))) →
              motive { nextAtIdx? := nextAtIdx? }) →
            (t : Std.IteratorAccess α m) → motive t