Definition be_le2 (be1 be2 : bool_expr) :=
  forall ve : var_env,
  bool_fun_of_bool_expr be1 ve = true -> bool_fun_of_bool_expr be2 ve = true.

Lemma BDDmu_ex_used_nodes_preserved : used_nodes_preserved cfg (fst (BDDmu_ex gc cfg ul nodet nodeg)) ul.