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Enriched categories, topoi, abelian categories, monoidal categories, homological algebra.

5 votes
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What is the intuitive difference between these two simplicial subdivision functors?

Lemma 2.2.11 in mn.uio.no/math/personer/vit/rognes/papers/aoms186-nocrop.pdf shows that the surjection you denote $sd(X) \to S(X)$ is an isomorphism if and only if $X$ is a non-singular simplicial set …
John Rognes's user avatar
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21 votes
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Is this an instance of the snake lemma?

Splice the left ends of the kernel-cokernel exact sequences $0 \to \ker(f) \to \ker(gf) \to \ker(g) \to \mathrm{cok}(f) \to \mathrm{cok}(gf) \to \mathrm{cok}(g) \to 0$ and $0 \to \ker(g) \to \ker(kg) …
John Rognes's user avatar
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10 votes

A question about Poincare duality

It is true. For ordinary cohomology this is a standard result about degree one maps; I think it is discussed at the beginning of Browder's book "Surgery on simply-connected manifolds". Let me treat e …
John Rognes's user avatar
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2 votes
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On the definition of infinity-category

Partial monoids (see Definition 2.2) play a useful role in Segal, Graeme Configuration-spaces and iterated loop-spaces. Invent. Math. 21 (1973), 213–221.
John Rognes's user avatar
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14 votes
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The "right" topological spaces

The convenient category CGH of compactly generated Hausdorff spaces has some poor colimits, since Hausdorffification may change the underlying point sets. The category CGWH of compactly generated we …
John Rognes's user avatar
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17 votes

Categorification of determinant

You can try to define the determinant of an $n \times n$ matrix with entries in a bipermutative (or symmetric bimonoidal) category $R$ by an analogue of the usual signed sum of $n$-fold products. Howe …
John Rognes's user avatar
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10 votes

What is the relation between the sphere spectrum and supersymmetry?

Like Schreiber does in his post, I would advertise the point of view developed by Sagave and Schlichtkrull in their Adv. Math 2012 paper, and used by us to study topological logarithmic geometry. Each …
John Rognes's user avatar
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5 votes
Accepted

Is there an ∞-categorical interpretation of the Quillen S⁻¹S construction?

A published reference for the claim (right after the question in boldface) is the proof given by Thomason on pages 1657-1658 of "First quadrant spectral sequences in algebraic K-theory via homotopy co …
John Rognes's user avatar
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