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'.