∀ {pat s : String.Slice} {stackPos needlePos : String.Pos.Raw},
  String.Slice.Pattern.Model.ForwardSliceSearcher.Invariants✝ pat s needlePos stackPos →
    needlePos = pat.rawEndPos → String.Slice.Pattern.Model.ForwardSliceSearcher.Invariants✝¹ pat s 0 stackPos