Section Components.
Variable cfg : BDDconfig.
Hypothesis cfg_OK : BDDconfig_OK cfg.
Definition bs_of_cfg := fst cfg.
Definition share_of_cfg := fst (snd cfg).
Definition fl_of_cfg := fst (snd (snd cfg)).
Definition cnt_of_cfg := fst (snd (snd (snd cfg))).
Definition negm_of_cfg := fst (snd (snd (snd (snd cfg)))).
Definition orm_of_cfg := fst (snd (snd (snd (snd (snd cfg))))).
Definition um_of_cfg := snd (snd (snd (snd (snd (snd cfg))))).

Lemma used_nodes_preserved_trans :
forall (cfg1 cfg2 cfg3 : BDDconfig) (ul : list ad),
BDDconfig_OK cfg1 ->
used_nodes_preserved cfg1 cfg2 ul ->
used_nodes_preserved cfg2 cfg3 ul -> used_nodes_preserved cfg1 cfg3 ul.