comment
Unoriented cobordism of oriented manifold
Chapter IX in Stong's "Notes on Cobordism Theory".
awarded
comment
Stable homology of general linear groups
Dwyer's paper is about homological stability. It does not contain a computation of a stable homology group.
awarded
revised
Loading…
Loading…
comment
"Inclusion" between higher categories of framed bordisms?
What is your definition of ``equivalence onto its image''?
comment
Classifying abelian (but non-central) group extensions using homotopy theory
The map $BAut(BA)\rightarrow BAut(A)$ is given by the action on $\pi_1(BA)$. Note that $A$ is abelian, so $\pi_1(BA)$ is functorial in unpointed maps.
comment
Classifying abelian (but non-central) group extensions using homotopy theory
Now one can compute $BAut(K(A,1))\simeq K(A,2)_{hAut(A)}$ and under this equivalence those fibrations whose monodromy over the basepoint agrees with the given action correspond to those pointed maps $BG\rightarrow K(A,2)_{hAut(A)}$ that induce the given action on fundamental groups.
comment
Classifying abelian (but non-central) group extensions using homotopy theory
$H^2(G;A)$ is the group of pointed homotopy classes of maps $BG\rightarrow K(A,2)_{hAut(A)}$ that induce the given action $G\rightarrow Aut(A)$ on fundamental groups (here the h-subscript denotes homotopy orbits). Fibrations over $BG$ with fibre $BA\simeq K(A,1)$ and an identification of the fibre over a fixed basepoint are classified by pointed maps $BG\rightarrow BhAut(K(A,1))$ where $Aut(K(A,1))$ is the topological monoid of self-homotopy-equivalences of $K(A,1)$.
comment
Spectral sequence construction of Euler class of group extension
Yes, up to a sign. This is a special case of Theorem 4 on p. 133 of Hochschild—Serre‘s ‘Cohomology of group extensions‘.
comment
What are some of the big open problems in $4$-manifold theory?
There will be a new list soon: aimath.org/workshops/upcoming/kirbylist
comment
The image of the J-homomorphism of the tangent bundle of the sphere
The relation follows from the discussion in Section 2 of James' "On the iterated suspension''.
comment
Monodromy action on homogeneous spaces
The fundamental group of the base of a fibre sequence acts on the fibre over the basepoint in the \emph{unpointed} homotopy category, so in general there is no induced action on the homotopy groups. The fundamental group of the total space however acts on the fibre in the \emph{pointed} homotopy category, and thus in particular on its homotopy groups. In your example, the action of $\pi_1(BG)=\pi_0(G)$ on $G/H$ is indeed given by left-translation, which is not pointed, but can be enhanced to a pointed action once one restricts it to $\pi_0(H)$ since $[1] \in G/H$ is now preserved.
awarded
comment
How to learn homotopy theory
That book has a second author.
comment
Poincaré duality
Less fancy, classical Lefschetz duality gives $H^q(M)\cong H^q(\overline{M})\cong H_{n-q}(\overline{M},\partial \overline{M})\cong \widetilde{H}_{n-q}(\overline{M}/\partial \overline{M})\cong \widetilde{H}_{n-q}(M^+)$.
comment
Relative version of Browder's theorem on H-spaces
Makes sense. Thanks.
comment
Relative version of Browder's theorem on H-spaces
$X=K(\mathbb{Z},2)$ is a counterexample to your first paragraph. Did you forget an assumption?