∀ (lhs rhs : String.Slice) (lstart rstart len : String.Pos.Raw) (h1 : len.offsetBy lstart ≤ lhs.rawEndPos)
  (h2 : len.offsetBy rstart ≤ rhs.rawEndPos),
  String.Slice.Pattern.Internal.memcmpSlice lhs rhs lstart rstart len h1 h2 =
    String.Slice.Pattern.Internal.memcmpStr lhs.str rhs.str (lstart.offsetBy lhs.startInclusive.offset)
      (rstart.offsetBy rhs.startInclusive.offset) len ⋯ ⋯