Definition BDDuniv_memo_put (cfg : BDDconfig) (x : BDDvar)
  (node node' : ad) :=
  match cfg with
  | (bs, (share, (fl, (cnt, (negm, (orm, um)))))) =>
      (bs, (share, (fl, (cnt, (negm, (orm, MapPut2 ad um node x node'))))))
  end.

Lemma used'_zero : forall (cfg : BDDconfig) (ul : list ad), used_node' cfg ul BDDzero.