&gt; C<i>-algebras are an esoteric subject—“the most abstract nonsense that exists in mathematics,” in Casazza’s words. “Nobody outside the area knows much about it.”<p>Wait what? C</i> algebras are <i>very</i> familiar to many doing quantum information, even those on the more experimental side. I don&#x27;t think they even make the top 10 for &quot;most abstract nonsense that exists in mathematics&quot;.