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Topology of cell complexes and manifolds, classification of manifolds (e.g. smoothing, surgery), low dimensional topology (e.g. knot theory, invariants of 4-manifolds), embedding theory, combinatorial and PL topology, geometric group theory, infinite dimensional topology (e.g. Hilbert cube manifolds, theory of retracts).

1 vote

Finiteness properties of general topological spaces

Let $X$ be a space, which we may as well assume connected. If $X$ is an ANR, then Milnor gives that $X$ is homotopy equivalent to a countable CW-complex $X'$. The question of when $X'$ is homotopy equ …
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0 votes

Lefschetz duality for twist coefficient

The Lefschetz duality is more naturally expressed as a duality between cohomology and homology. An oriented $n$-manifold with boundary has a fundamental class $[M]\in H_n(M,\partial M;\mathbb{Z})$, an …
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10 votes

Covering manifolds with some other manifolds

A first observation is that such a $k$ may not exist, for example if $N$ does not embed in $M$. When $N$ is a disk, then $k$ equals the ball category of $M$, denoted $\operatorname{ballcat}(M)$ or $\ …
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8 votes

Triangulations of submanifolds of smooth manifolds

It follows from Verona's solution to Thom's triangulation conjecture that the inclusion $N\hookrightarrow M$ is triangulable whenever it is proper and topologically stable, and $M$ and $N$ are without …
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15 votes
Accepted

What is the 'non-intuitive' part in sphere eversion (turning inside out)?

Watch Outside In (something we should all do anyway, to commemorate Bill Thurston's passing). To understand the mathematics behind sphere eversions, you should first get a good intuition for the conc …
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11 votes

Which closed orientable $4$-dimensional manifolds cannot be embedded in $6$-space?

$\mathbb{C}P^2$ does not embed in $\mathbb{R}^6$. See Feder, S.; Segal, D. M. Immersions and embeddings of projective spaces, Proc. Amer. Math. Soc. 35 (1972), 590–592.
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2 votes

manifolds with unusual rational cohomology rings

I'm not sure if this is quite what you're looking for, because: (a) it's a $3$-manifold with boundary, and (b) it's not the ring structure which is interesting; but the Borromean Rings link compl …
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2 votes
Accepted

Definition of Milnor exact sequence and complex-oriented generalized cohomology of $\mathbb{...

Milnor's paper is called On axiomatic homology theory and is published in Pacific J. Math. Volume 12, Number 1 (1962), 337-341. It is also reprinted in Frank Adams' Algebraic Topology: A Student's Gui …
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3 votes

Homotopy Extension Property (HEP)

You need a relative version of the Isotopy Extension Theorem. There is a proof of the non-relative version in Hirsch's "Differential Topology", pp. 177-180. Perhaps more relevant to your question is t …
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1 vote

Identifying the orientation bundle uniquely

Any connected orientable surface $X$ which doubly covers $S$ must be homeomorphic to the orientation cover $\tilde{S}$. Proof: Connected orientable surfaces are classified up to homeomorphism by th …
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5 votes
Accepted

important vector bundles

The top exterior power of the tangent bundle determines orientablility (the most basic of topological invariants, after dimension) in the sense that $\wedge^nTM$ is a trivial line bundle iff $M^n$ is …
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1 vote

Regular homotopy invariance of Wall's self-intersection form.

I don't know about a rigorous proof, but here is a heuristic explanation you may find helpful. You have a compact $1$-dimensional manifold given by the self-intersections of the trace $f$ of your reg …
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3 votes
Accepted

Thom's result and Poincaré duality

Let me attempt to answer your question as I understand it. Let $x\in H^1(M)$ be the Poincaré dual of $[c]\in H_1(M)$ (all (co)homology groups are with $\mathbb{Z}_2$ coefficients). The result of Thom …
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4 votes

Fake projective spaces

The Manifold Atlas page http://www.map.mpim-bonn.mpg.de/Fake_complex_projective_spaces has plenty of useful information and references.
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21 votes
Accepted

Link such that deleting any two components leaves an unlink

Yes, this is done in Penney, D.E., Generalized Brunnian links, Duke Math. J. 36, 31-32 (1969). ZBL0176.22201. Call a link $(n,k)$-Brunnian if it has $n$ components, and every sublink with $m$ compo …
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