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• CommentRowNumber1.
• CommentAuthorUrs
• CommentTimeMay 29th 2012

I have created stratified space in order to collect some references

• CommentRowNumber2.
• CommentAuthorDavid_Corfield
• CommentTimeMay 29th 2012

I see that links to the fundamental category with duals of a stratified space. That old Cafe discussion led to a paper by Woolf, as John mentioned here. It’s Transversal homotopy theory.

Did anything come of that?

• CommentRowNumber3.
• CommentAuthorzskoda
• CommentTimeMay 29th 2012
• (edited May 29th 2012)

• M. Banagl, Topological invariants of stratified spaces, Springer Monographs in Math. 2000.

As a graduate student in Wisconsin, I was among the guinea pigs who listened an excellent and clear exposition by the author of parts of the notes (directed toward the intersection cohomology) , before they were finalized.

• CommentRowNumber4.
• CommentAuthorDavidRoberts
• CommentTimeJun 1st 2012

@David - I’m not sure, but Lurie has some material in appendix A to Higher Algebra on what he calls the exit-path $\infty$-category. I think this is a generalisation of the 2-category described by Treumann in arXiv:0708.0659 and the results therein. Essentially representations of the exit path $\infty$-category in $\infty Gpd$ are the same as constructible $\infty$-sheaves, generalising the case of representations of the fundamental $\infty$-groupoid being the same as locally constant $\infty$-sheaves. This is of course a massive generalisation of the old result that representations of the fundamental groupoid in $Set$ give covering spaces.

I should say that ’constructible’ just means ’locally constant on each stratum’. The 1-stack of perverse sheaves (a subcategory of the derived category of coherent sheaves) is an example of a constructible 1-stack.

There is a van Kampen theorem for the exit-path $\infty$-category, which I like to think of as the ultimate version of Ronnie Brown’s work on van Kampen-type results on filtered spaces (which give rise to a natural stratification).

• CommentRowNumber5.
• CommentAuthorDavid_Corfield
• CommentTimeJun 1st 2012

So the Baez-Dolan approach is different. Paths cross strata, not just exit them. Woolf had already done something along the lines of Treumann.