public void applyWith(BDD that, BDDOp opr) {
public BDD applyWith(BDD that, BDDOp opr) {
        public void applyWith(BDD that, BDDOp opr) {            int x = _index;            int y = ((bdd) that)._index;            int z = opr.id;            int a = bdd_apply(x, y, z);            //System.out.println("applyWith("+System.identityHashCode(this)+", "+System.identityHashCode(that)+") "+x+","+y+" -> "+a);            bdd_delref(x);            if (this != that)                that.free();            bdd_addref(a);            this._index = a;        }