∀ {pat s : ByteArray} {stackPos needlePos : ℕ},
  String.Slice.Pattern.Model.ForwardSliceSearcher.PartialMatch✝ pat s needlePos stackPos →
    ∀ {needlePos' : ℕ},
      String.Slice.Pattern.Model.ForwardSliceSearcher.PartialMatch✝¹ pat pat needlePos' needlePos ↔
        needlePos' ≤ needlePos ∧
          String.Slice.Pattern.Model.ForwardSliceSearcher.PartialMatch✝² pat s needlePos' stackPos