Definition BDDmake :=
if Neqb l r
then (cfg, l)
else
match MapGet3 _ (fst (snd cfg)) l r x with
| Some y => (cfg, y)
| None => BDDalloc gc cfg x l r ul
end.

Lemma BDDmake_preserves_used_nodes :
used_nodes_preserved cfg (fst BDDmake) ul.