∀ {s : String.Slice} (motive : Option s.Pos → Sort u_1) (h_1 : (pos : s.Pos) → none = some pos → motive (some pos))
  (h_2 : none = none → motive none),
  (match hd : none with
    | some pos => h_1 pos hd
    | none => h_2 hd) =
    h_2 ⋯