if (set2.contains(e)) {
            size++;
          }
        }
        return size;
      }

      @Override
      public boolean isEmpty() {
        return Collections.disjoint(set2, set1);
      }

      @Override
      public boolean contains(@CheckForNull Object object) {
        return set1.contains(object) && set2.contains(object);
      }

      @Override