Re: How can we have a categorical definition of "theory"

Dear Patrik, It's absolutely vital to Grothendieck's idea of toposes as generalized spaces. It's essentially categorical logic that allows you to think of toposes as spaces and geometric morphisms as continuous maps. For an introduction, see my TACL talks http://www.cs.bham.ac.uk/~sjv/talks.php particularly numbers 1-4 (the Olomouc tutorials). Steve. On 10/11/2017 16:49, peklund@cs.umu.se wrote:

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Categorical "logic" in a topos to me makes no practical sense at all.

Patrik

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