Computing an integer using a Grothendieck topos
&gt; Johnstone&#x27;s topological topos is very easy to describe: take the monoid of continuous endomaps of the one-point compactification of the discrete natural numbers, considered as a category, then take sheaves for the canonical coverage.<p>I really wish technical authors wouldn&#x27;t say &quot;very easy&quot; when they mean &quot;readers will need a substantial intellectual investment such as a Ph.D&quot;.