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@ 2008-08-19 14:45 John Baez
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From: John Baez @ 2008-08-19 14:45 UTC (permalink / raw)
  To: categories

Dear Categorists -

Given a category C with pullbacks we can define a bicategory Span(C)
where objects are objects of C, morphisms are spans - composed
using pullback - and 2-morphisms are maps between spans.

Have people tried to categorify this yet?

Suppose we have a 2-category C with pseudo-pullbacks.  Then we should
be able to define a tricategory Span(C).   Has someone done this?

Or maybe people have gotten some partial results, e.g. in the case
where C = Cat.  I'd like to know about these!

Best,
jb






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