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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).

11 votes

extension of surface homeomorphism

You can find a proof of this in the paper MR1885215 (2002m:57019) Leininger, Christopher J.(1-TX); Reid, Alan W.(1-TX) The co-rank conjecture for 3-manifold groups. (English summary) Algebr. Geom. …
Andy Putman's user avatar
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26 votes

Thurston's "tinker toy" problem

It was published here: M. Kapovich, J. Millson, Universality theorems for configuration spaces of planar linkages, Topology 41 (2002), no. 6, 1051–1107.
Andy Putman's user avatar
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6 votes
Accepted

Homotopies with prescribed regular values

The answer is "yes" if $M_1$ is compact. Here's a sketch of a proof. Consider any smooth homotopy $G:M_1 \times I \rightarrow M_2$ between $f_0$ and $f_1$. Since $M_1$ is compact, the set of regula …
Andy Putman's user avatar
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10 votes
Accepted

What does the matrix of a mapping class tell you about the 3-manifold?

In addition to the first homology group, it also determines the Seifert pairing on the torsion in the first homology group. What is more, in an appropriate sense this is all it determines. This is a …
Andy Putman's user avatar
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7 votes

Homology generated by lifts of simple curves

I just posted a paper with Justin Malestein entitled "Simple closed curves, finite covers of surfaces, and power subgroups of $\text{Out}(F_n)$" that gives a nearly complete answer to this question. …
Andy Putman's user avatar
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9 votes

Teichmuller theory and moduli of Riemann surfaces

I'll discuss things which are more applications of the mapping class group to moduli space rather than Teichmuller theory per se, but of course this is all tightly connected. One of the big applicati …
Andy Putman's user avatar
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4 votes

Jordan Curve Homotopy

At least in dimension 2, results like this are true in great generality. A Jordan curve in the plane is simply an embedded curve. In other surfaces, we have that two simple closed curves $\gamma_1$ …
Andy Putman's user avatar
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5 votes
Accepted

Resource for Measured Foliations and Whitehead Equivalence

I don't know of a source other than FLP for understanding the Thurston compactification via measured foliations, but you might find it easier to understand this compactification using measured geodesi …
Andy Putman's user avatar
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10 votes

Maximal euler characteristic of surfaces bounding two fixed curves

For orientable surfaces of genus at least $2$, pretty sharp bounds are obtained in the unpublished PhD thesis of Ingrid Irmer, which is available here.
Andy Putman's user avatar
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4 votes

Surface automorphisms and conformal automorphisms

It was proven in J. MacCarthy and A. Papadopoulos. Involutions in surface mapping class groups. Enseign. Math. 33 (1987), 275–290. that the mapping class group is generated by the conjugates of a si …
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4 votes
Accepted

a CW-complex homotopic to a manifold

For this to be true, you need to assume that your $4$-manifold $M$ is not a compact nonorientable manifold. Otherwise, you would have $H_4(M;\mathbb{Q}) = 0$ but $H_4(M;\mathbb{Z}/2) \neq 0$, so ther …
Andy Putman's user avatar
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17 votes
Accepted

Homotopy type of the plane minus a sequence with no limit points

Yes. More generally, if $X$ is a proper closed subset of $\mathbb{R}^2$, then every path component $M$ of $\mathbb{R}^2 \setminus X$ is homotopy equivalent to a wedge of circles (observe that $X$ mig …
Andy Putman's user avatar
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5 votes
Accepted

Normal generation of Torelli

For the Torelli group of a surface, I gave a much easier and more geometric proof in my paper MR2302503 (2008c:57049) Putman, Andrew(1-CHI) Cutting and pasting in the Torelli group. (English summary …
Andy Putman's user avatar
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7 votes

How many different knot types can have the same shadow (projection)

There exist projections with any number of crossings such that any choices of over/under crossings gives the unknot. I am writing on my phone and cannot draw a picture, but here is a description of o …
Andy Putman's user avatar
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4 votes

Reference request: Reidemeister type moves for immersed curves on surfaces

This isn't true as stated. What is true is that if $\gamma$ and $\gamma'$ two homotopic curves that are in minimal position (i.e. each contains the minimal number of self-intersections in their homot …
Andy Putman's user avatar
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