public void restrictWith(BDD var) {
public BDD restrictWith(BDD var) {
        public void restrictWith(BDD var) {            BDD c1 = ((TestBDD)var).b1;            BDD c2 = ((TestBDD)var).b2;            b1.restrictWith(c1);            b2.restrictWith(c2);            assertSame(b1, b2, "restrict");        }