They wrote a book, The UNIX Programming Environment. It's one of the classics of UNIX literature; one that I heartily recommend (despite its relative age) because it stresses the why of UNIX-oriented approaches to problem-solving in general, and programming in particular.
Anyway, as I was reading my (first) copy, I encountered something that I found peculiar. Being somewhat young and foolish, as well as direct, I wrote them a letter.
I was a little surprised to receive a letter with a return address in New Jersey a few weeks later. I've scanned the letter, and thus reproduced it for you: