(* not this version! Lemma sublist_list_repeat {A} i j k (v:A) (I: 0<=i) (IJK: (Z.to_nat i <= Z.to_nat j <= k)%nat): sublist i j (list_repeat k v) = list_repeat (Z.to_nat (j-i)) v. *)

Lemma sublist_rejoin':
forall {A} lo mid mid' hi (al: list A),
mid=mid' ->
0 <= lo <= mid ->
mid' <= hi <= Zlength al ->
sublist lo mid al ++ sublist mid' hi al = sublist lo hi al.