∀ {σ : String.Slice → Type} {ρ : Type} {pat : ρ} {s : String.Slice}
  [inst : String.Slice.Pattern.ToBackwardSearcher pat σ] (currPos : s.Pos)
  (searcher : Std.Iter (String.Slice.Pattern.SearchStep s)) (currPos_1 : s.Pos)
  (searcher_1 : Std.Iter (String.Slice.Pattern.SearchStep s)),
  (String.Slice.RevSplitIterator.operating currPos searcher =
      String.Slice.RevSplitIterator.operating currPos_1 searcher_1) =
    (currPos = currPos_1 ∧ searcher = searcher_1)