Hint Rewrite @upd_Znth_app1 using list_solve : sublist.
Hint Rewrite @upd_Znth_app2 using list_solve : sublist.

Lemma nth_Znth {A} {d: Inhabitant A}:
forall n (xs:list A), 0 <= n < Zlength xs -> (nth (Z.to_nat n) xs d) = (Znth n xs).