[nimrody]

"Typeset by the authors in Minion Pro, Lato, and Consolas, using Go, groff, ghostscript, and a host of other open-source Unix tools. Figures were created in Google Drawings."

groff still going strong... although it seems like Kernighan got tired of drawing using the 'pic' language...

[copperx]

Yep, I was really curious to see if he had finally given up and gone to TeX, Indesign, or the like.

I guess that if one's not dealing with a lot of math, groff is enough for many typesetting jobs.

I'm curious as to which version of groff they used. Heirloom groff? GNU groff? hmm...

[eric_the_read]

groff == GNU roff by definition. I suspect by "Heirloom groff" you mean troff or nroff.