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

Lemma BDDvar_make_keeps_neg_memo_OK : forall (cfg : BDDconfig) (negm : BDDneg_memo) (x : BDDvar), BDDconfig_OK cfg -> BDDneg_memo_OK_2 cfg negm -> BDDneg_memo_OK_2 (fst (BDDvar_make cfg x)) negm.