(*Prior to block := Z, the lemma as like this: Lemma find_symbol_add_globals: forall {F V} i g id dl, ~ In i (map fst dl) -> list_norepet (map fst dl) -> (Genv.find_symbol (Genv.add_globals (Genv.empty_genv F V) (dl ++ (i, g) :: nil)) id = Some (1 + Zlength dl) <-> i = id). *)

Lemma nth_error_app1: forall {T} (al bl : list T) (j: nat),
(j < length al)%nat ->
nth_error (al++bl) j = nth_error al j.