∀ {m : Type w → Type w'} [inst : Monad m] {β : Type w} {array : Array β} {pos : ℕ},
  (array.iterFromIdxM m pos).step =
    pure
      (Std.Shrink.deflate
        (if h : pos < array.size then Std.PlausibleIterStep.yield (array.iterFromIdxM m (pos + 1)) array[pos] ⋯
        else Std.PlausibleIterStep.done ⋯))