Definition nodes_preserved (cfg cfg' : BDDconfig) :=
  forall (x : BDDvar) (l r node : ad),
  MapGet _ (fst cfg) node = Some (x, (l, r)) ->
  MapGet _ (fst cfg') node = Some (x, (l, r)).

Lemma BDDneg_memo_OK_lemma_1_4' : forall (cfg : BDDconfig) (memo : BDDneg_memo) (node node' : ad), BDDconfig_OK cfg -> BDDneg_memo_OK_2 cfg memo -> config_node_OK cfg node -> BDDneg_memo_lookup memo node = Some node' -> config_node_OK cfg node'.