return delegate().setCount(element, count);
      }
    }

    @Override
    public boolean setCount(@ParametricNullness E element, int oldCount, int newCount) {
      synchronized (mutex) {
        return delegate().setCount(element, oldCount, newCount);
      }
    }

    @Override
    public Set<E> elementSet() {
      synchronized (mutex) {
        if (elementSet == null) {