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_1 :
Neqb l r = true ->
Neqb (node_height (fst BDDmake) (snd BDDmake)) (node_height cfg l) = true.