∀ (motive : String.Legacy.Iterator → Char → Sort u_1) (s : String) (i : String.Pos.Raw) (c : Char)
  (h_1 : (s : String) → (i : String.Pos.Raw) → (c : Char) → motive { s := s, i := i } c),
  (match { s := s, i := i }, c with
    | { s := s, i := i }, c => h_1 s i c) =
    h_1 s i c