{s : String.Slice} →
  {p : String.Pos.Raw} →
    {motive : String.Pos.Raw.IsValidForSlice s p → Sort u} →
      (t : String.Pos.Raw.IsValidForSlice s p) →
        ((le_rawEndPos : p ≤ s.rawEndPos) →
            (isValid_offsetBy : String.Pos.Raw.IsValid s.str (p.offsetBy s.startInclusive.offset)) → motive ⋯) →
          motive t