I delighted in this article because of its opinions about what is easy and what is hard. Physics engine: easy; of course you have one; everyone has a physics engine. Graph data structure &amp; algos: suggests a few places to find one.<p>As an older programmer who is in the midst of retooling, I would assume the opposite: graphs easy, physics hard. But that&#x27;s what retooling seems to be all about -- finding the new &quot;easy&quot; and learning it.