The @CAT Seminar

The forty-fifth anniversary of the category seminar seems like a good time to recall its genesis. In 1971, I had taken up my position as assistant professor at Dalhousie and Dietmar Schumacher had done the same at Acadia. Since my graduate student days, participating in the Lambek seminar, I had been a strong proponent of seminars. So feeling the shock of isolation after very active postdoctoral appointments, we hatched the idea of running one of our own. So, in 1972, with the recently arrived graduate student Richard Wood, we started a weekly seminar on the new hot topic, topos theory. Apart from Richard, Dietmar and me, there were Luzius Grunenfelder, Tony Thompson, Maureen Fitzpatrick (now Tingley) and Ioana Schiopu, and perhaps others. After covering the basics, we tackled the construction of the real numbers object in a topos with the aim of establishing the theorem that in a topos of sheaves on a space, the reals consisted of continuous functions on that space. We ran into some difficulties which we couldn't resolve. It turned out that the original definition was not quite correct.

The following year, Ioana had left but we were joined by a new graduate student, Bob Rosebrugh, who turned out to be one of the seminar's most faithful adherents. The early days saw a variety of participants, the most active of which was David Lever. Others that come to mind are Peter Schotch from philosophy, Phil Scott and, a bit later, Robert Dawson.

There were many visitors passing through and they usually wanted to give a talk in "the seminar". A couple of Australians that "stick out" in my memory are Bob Walters (who initiated us to this new thing called email) and Ross Street, but there were many others, too many to mention.

At some point in the early 80's the department decided that future development would be in areas where there were strong research groups, so we identified ourselves as the "Algebra and Category Group". It consisted of Luzius Grunenfelder, Pat Stewart, Richard Wood (who was now a faculty member) and myself.

By then, Bob Rosebrugh was on the faculty at Mount Allison and would drive down every week (!) to collaborate with Richard and participate in the seminar. By my estimate, he and Dietmar have driven over 300,000 kilometers in the service of category theory.

Most of the talks were at Dalhousie but, from time to time, we had a full day of talks at Acadia, Mount Allison or Saint Mary's. These were always memorable outings. We were truly a Maritimes' seminar. In 1991-92, it happened that 75% of the math department at the Grenfell campus of Memorial University in Corner Brook, Newfoundland, were category theorists. The department consisted of Jonathon Funk, Richard Squire on term appointments and Rick MacLeod, all category theorists. The rest of the department consisted of Ron Richards, a McMaster-trained algebraist, so our "honorary category theorist". In May 1992, we had a two day seminar there. We could now claim to be an Atlantic Canadian seminar and we adopted the name "The Atlantic Canada Category Seminar", or ATCAT for short, which has become @CAT, in this age of the internet.

The seminar talks since 1985 have been well-documented at Previous years. Clicking the links there will give an idea of the visitors we've hosted and the variety of topics covered. Apart from category theory as such, there have been talks on algebra, topology, logic, computer science and physics, all with a slight categorical accent.