Definition BDDvar_le := Nleb.
Definition BDDvar_max (x y : BDDvar) := if BDDvar_le x y then y else x.

Lemma BDDvar_ordered_low_1 :
forall (cfg : BDDconfig) (node1 node2 : ad),
BDDconfig_OK cfg ->
is_internal_node cfg node1 ->
is_internal_node cfg node2 ->
is_internal_node cfg (low cfg node1) \/ is_internal_node cfg (low cfg node2) ->
BDDcompare (BDDvar_max (var cfg (low cfg node1)) (var cfg (low cfg node2)))
(BDDvar_max (var cfg node1) (var cfg node2)) = Datatypes.Lt.