How did dennis ritchie produce his PhD thesis?: a typographical mystery

Dennis Ritchie, the creator of the C programming language and, with Ken Thompson, the co-creator of the Unix operating system, completed his Harvard PhD thesis on recursive function theory in early 1968. But for unknown reasons, he never officially received his degree, and the thesis itself disappeared for nearly 50 years. This strange set of circumstances raises at least three broad questions: • What was the technical contribution of the thesis? • Why wasn't the degree granted? • How was the thesis prepared? This paper investigates the third question: how was a long and typographically complicated mathematical thesis produced at a very early stage in the history of computerized document preparation?