∀ (pat pat_1 : ByteArray) (e_pat : pat = pat_1) (stackPos stackPos_1 : ℕ) (e_stackPos : stackPos = stackPos_1)
  (hst : stackPos < pat.size),
  String.Slice.Pattern.Model.ForwardSliceSearcher.prefixFunction✝ pat stackPos hst =
    String.Slice.Pattern.Model.ForwardSliceSearcher.prefixFunction✝¹ pat_1 stackPos_1 ⋯