Hint Rewrite @sublist_nil' using list_solve: sublist.
Hint Rewrite @app_nil_l : sublist.
Hint Rewrite @Zlength_rev : sublist.
Hint Rewrite @sublist_rejoin' using list_solve : sublist.

Lemma upd_Znth_app2 {A} (l1 l2:list A) i v:
Zlength l1 <= i <= Zlength l1 + Zlength l2 ->
upd_Znth i (l1 ++ l2) v = l1 ++ upd_Znth (i-Zlength l1) l2 v.