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_node_height_eq :
Neqb l r = false ->
Neqb (node_height (fst BDDmake) (snd BDDmake)) (ad_S x) = true.