Way late - I'm actually a chapter ahead - but onward we go, with
Inspector Kusanagi and hanger-on Kishitani are visiting Teito university and Dr. Yugawa. They've just returned from another interview with Yasuko Hanaoka where she apparently conveniently solidified her convenient movie alibi with some convenient ticket stubs, conveniently forgotten in the conveniently saved movie program. This level of convenience did not pass unnoticed by our hawk-eyed inspector; nor is it overlooked by our all-around genius Yugawa. Convenient but, as Yugawa points out, not unreasonable.
Over coffee, Kusanagi mentions Ishikami in passing, and wonders whether he by any chance would be Yugawa's senior at university. A bit of banter and a yearbook picture later it transpires that Ishikami and Yugawa not only were undergraduate classmates, but Kishigami was in fact famous among his fellow students and faculty as an exceptionally bright mathematician. As a budding physicist, Yugawa and Kishigami went on separate course tracks but even so Yugawa got to hear about Kishigami's exploits. Eschewing computers he'd stay late into the night with just a notebook and pencil to work on some problem. Thus Yugawa is astonished to hear that his illustrious classmate is not a university professor or researcher, but a high school teacher.
Cut to Ishigami, who goes out on his (apparently common) trek to the nearby phone booth. He even meets Yasuko in the stairs, but rather than exchange words in the stairwell he has to be all cloak-and-dagger conspicuous with phone booths, telephone cards and sideways glances. I'm surprised the author doesn't have them use code words. Anyway (I promise I'll quit harping on this), Ishigami hears her side of the latest developments; she gave them the movie ticket stubs in a hopefully natural manner, and they asked her daughter Misato for confirmation on what they did that day.
Walking back home, Ishigami sees a tall shape waiting in the doorway. It is not a dead friend come back from his grave to warn him of his folly (this is not a Stephen King novel after all), but none other than our hero Yugawa, come to drop in on his long lost school mate. The circle is complete, the student is the master.