[mac_truck]

It was a single sentence offered as one single example of the book's contents. It appeared halfway through the article and well after the authors had twice explicitly identified the topic of their book:

Hmm, not too good with discrete concepts are you?

Perhaps you should undergo some thematic appreciation testing to determine what the problem might be. (lol).

[GOPcapitalist]

Question what you may, mac, but just remember that you're the one who, when asked to pick out the topic sentence, ignored the words of the authors themselves essentially saying "here is our topic sentence: ..." and instead opted for an awkwardly placed passage appearing halfway through the article that also just happened to express an opinion that persons of your well known personal biases would find appealing.