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_char {A} n l1 (v:A) l2 w: Zlength l1=n ->
upd_Znth n (l1 ++ v :: l2) w = l1 ++ w :: l2.