Definition BDDvar_make (cfg : BDDconfig) (x : BDDvar) :=
BDDmake cfg x BDDzero BDDone.

Lemma BDDvar_make_preserves_nodes :
forall (cfg : BDDconfig) (x : BDDvar),
BDDconfig_OK cfg -> nodes_preserved cfg (fst (BDDvar_make cfg x)).