It was at this time that he had his only formal research students, of whom J. W. S. Cassels was one. His idea of supervising research was said to involve the suggestion that a proof of the transcendence of the Euler–Mascheroni constant was probably worth a doctorate. His book "Diophantine Equations" (1969) is based on lectures, and gives an idea of his discursive style. Mordell is said to have hated administrative duties. While visiting the University of Calgary, the elderly Mordell attended the Number Theory seminars and would frequently fall asleep during them. According to a story by number theorist Richard K. Guy, the department head at the time, after Mordell had fallen asleep, someone in the audience asked "Isn't that Stickelberger's theorem?" The speaker said "No it isn't." a few minutes later the person interrupted again and said "I'm positive that's Stickelberger's theorem!" The speaker again said no it wasn't. The lecture ended, and the applause woke up Mordell, and he looked up and pointed at the board, saying "There's old Stickelberger's result!"