{ρ : Type} →
  {ρ_1 : ρ} →
    {σ : String.Slice → Type} →
      [inst : String.Slice.Pattern.ToBackwardSearcher ρ_1 σ] →
        {s : String.Slice} → String.Slice.RevSplitIterator ρ_1 s → Option (Std.Iter (String.Slice.Pattern.SearchStep s))