Section BDDunivl_results.
Variable cfg : BDDconfig.
Variable ul : list ad.
Variable node : ad.
Variable ly : list BDDvar.
Hypothesis cfg_OK : BDDconfig_OK cfg.
Hypothesis ul_OK : used_list_OK cfg ul.
Hypothesis used : used_node' cfg ul node.

Lemma BDDunivl_used_nodes_preserved :
used_nodes_preserved cfg (fst (BDDunivl cfg ul node ly)) ul.