End BDDand_results.
Section BDDiff_results.
Variable cfg : BDDconfig.
Variable ul : list ad.
Variable node1 node2 : ad.
Hypothesis cfg_OK : BDDconfig_OK cfg.
Hypothesis ul_OK : used_list_OK cfg ul.
Hypothesis used1 : used_node' cfg ul node1.
Hypothesis used2 : used_node' cfg ul node2.
Definition BDDiff :=
match BDDor cfg ul node1 node2 with
| (cfg1, node3) =>
match BDDand cfg1 (node3 :: ul) node1 node2 with
| (cfg2, node4) => BDDimpl cfg2 (node4 :: node3 :: ul) node3 node4
end
end.

Lemma BDDiff_used_nodes_preserved : used_nodes_preserved cfg (fst BDDiff) ul.