<i>X&#x2F;Z are used in the &#x27;program structure&#x27; example without introducing them beforehand</i><p>Probably intentional. A big part of the skill of reverse-engineering that they&#x27;re introducing here is the feeling of &quot;I don&#x27;t understand what this line does, so I&#x27;ll just accept it and move on, and see if I understand it later&quot;. Using X&#x2F;Z before describing it is definitely in keeping with that feeling.<p>The whole document reads as &quot;we&#x27;re intentionally throwing you in the deep end by giving you not quite enough to understand completely, but giving you enough that you can understand with some work&quot;. It&#x27;s a similar approach to Microcorruption, and to the crypto challenges. I like it.