are you applying to computer science programs or math programs? for category theory, you might look at where the Ken Shans of the world went to grad school. for diff geo, there are a host of great places. and I don't know exactly what you mean by diff geo. You could be into gauge theory, in which case places like Imperial College, Cambridge, Oxford, Columbia, Duke, MIT come to mind (advisors like Donaldson, Hamilton, Morgan, Bryant, dozens I'm neglecting to mention). The other standard top US schools (Harvard, Princeton, Stanford, Berkeley, Chicago, Michigan) are all pretty strong in both algebra and geometry, of course (Yau, Givental, Eliashberg, etc, are at these schools). Other places like UT Austin, Northwestern, UIUC, UCLA, and even UW (University of Washington) come to mind. In Canada, UBC. Also, you may find that your interests are closer to (say) algebraic geometry, which is intimately connected to the kind of diff geo that's done in relation to physics these days. In which case you might want to consider Chicago and Northwestern strongly, as these schools have amazing alg geo groups these days. Of course Harvard is the historical leader here (some have left, but Mumford, Mazur, Yau, Griffiths, Harris, Siu, Richard Taylor, etc), and Princeton is also incredibly strong. Pretty much any of these schools will give you a plenty strong background in category theory to understand it for haskell, I'd say (perhaps this is overstatement, but (for example) algebraic geometers tend to become quite expert at category theory). On Fri, 13 Jul 2007, Creighton Hogg wrote:

Hi Haskell, Sorry to contribute to the noise but given that we've been talking about categories lately, I was wondering if anyone had any opinions on good universities for studying category theory. I'm trying to figure out where to apply for my phd. I want to either be at a place with a strong category theory program or a strong differential geometry program.

Thanks, Creighton