How do you put an object on multiple different lists with this technique?<p>E.g. in FreeBSD an mbuf can be on two lists at once: <a href="http:&#x2F;&#x2F;svnweb.freebsd.org&#x2F;base&#x2F;head&#x2F;sys&#x2F;sys&#x2F;mbuf.h?revision=293439&amp;view=markup#l178" rel="nofollow">http:&#x2F;&#x2F;svnweb.freebsd.org&#x2F;base&#x2F;head&#x2F;sys&#x2F;sys&#x2F;mbuf.h?revision=...</a>