∀ {s : String.Slice} (pos : s.Pos) (motive : Option (s.sliceTo pos).Pos → Sort u_1) (nextCurr : (s.sliceTo pos).Pos)
  (h_1 : (nextCurr : (s.sliceTo pos).Pos) → motive (some nextCurr)) (h_2 : (x : Option (s.sliceTo pos).Pos) → motive x),
  (match some nextCurr with
    | some nextCurr => h_1 nextCurr
    | x => h_2 x) =
    h_1 nextCurr