Skip to main content
Search type Search syntax
Tags [tag]
Exact "words here"
Author user:1234
user:me (yours)
Score score:3 (3+)
score:0 (none)
Answers answers:3 (3+)
answers:0 (none)
isaccepted:yes
hasaccepted:no
inquestion:1234
Views views:250
Code code:"if (foo != bar)"
Sections title:apples
body:"apples oranges"
URL url:"*.example.com"
Saves in:saves
Status closed:yes
duplicate:no
migrated:no
wiki:no
Types is:question
is:answer
Exclude -[tag]
-apples
For more details on advanced search visit our help page
Results tagged with
Search options answers only not deleted user 1345

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).

8 votes
Accepted

Preserving non-conjugacy of loxodromic isometries in a Dehn filling

It follows from the comment of Moisha Kohan above. Another way to see it: take the closed oriented geodesics $\gamma, \eta$ in $M$ realizing the monodromy of $g$ and $h$ respectively. Since $g$ and $h …
Ian Agol's user avatar
  • 68.9k
7 votes

Does every mapping class group embed into some $\mathrm{Out}(F_n)$?

$\DeclareMathOperator\Mod{Mod}\DeclareMathOperator\GL{GL}\DeclareMathOperator\Out{Out}$It is true for $g=1,2$. $\Mod(S_1) \cong \GL_2(\mathbb{Z})\cong \Mod(S_{1,1})\cong \Out(F_2)$. In $\Mod(S_2)$, th …
YCor's user avatar
  • 63.9k
1 vote

Necessary condition for invertible knot concordance from both ends

Let $C$ denote a concordance from $K_1$ to $K_2$ in $S^3\times [0,1]$, and let $C_1, C_2$ be concordances from $K_2$ to $K_1$. Let $C_1 \cdot C \sim K_2 \times [0,1]$, $C\cdot C_2\sim K_1\times [0,1]$ …
Ian Agol's user avatar
  • 68.9k
4 votes
Accepted

Slice-ribbon conjecture in other 3-manifolds

One may still ask for the disk to be “ribbon” in $M\times [0,1]$ in the sense that the projection of $M×[0,1]$ to $[0,1]$ is a Morse function when restricted to the disk with only index 1 and 2 critic …
Ian Agol's user avatar
  • 68.9k
1 vote

Classifying nested 3-manifolds with fundamental group property

The only sort of examples that I can imagine are when there is a handlebody $H$ such that $M_1\subset H \subset M_2$. It holds more generally when $\pi_1(M_2-M_1)\to \pi_1(M_2)$ is onto. This might al …
Ian Agol's user avatar
  • 68.9k
4 votes

Is there a way to classify incompressible surfaces in $\Sigma \times [0,1]$ ?

Since you are asking for incompressible but not $\partial$-incompressible, the classification is more complicated. As pointed out in Sam Nead's answer, the classification of incompressible and boundar …
Ian Agol's user avatar
  • 68.9k
4 votes
Accepted

The diameter of the projection of a convex core

Take a Schottky group $\Gamma$ with convex core $N\subset \mathbb{H}^3/\Gamma$ with $diam(N)$ large, but $diam(\partial N)$ bounded. Then by a theorem of Robert Brooks, there is a small deformation $\ …
Ian Agol's user avatar
  • 68.9k
23 votes

$3$-manifold that is a surgery on a knot

This is an extensively studied question and is far from being understood in general. Here are some other conditions beyond the fact that $H_1(M)$ is cyclic. the fundamental group should have weight 1 …
Ian Agol's user avatar
  • 68.9k
5 votes

Existence of a surface group ensures the existence of a $\pi_1$-injective immersed surface

Given a $CW$-complex $X$ and a closed surface group $\pi_1(\Sigma,v) < \pi_1(X,x)$, there exists a map $\phi: (\Sigma,v) \to (X,x)$ such that the image of the fundamental group is this subgroup. Take …
Sam Nead's user avatar
  • 28.2k
3 votes

Residual finiteness of hyperbolic 3-manifold groups

The answer to Q1 is negative in general (allowing infinitely generated fundamental group). See Example 2 which is a discrete torsion-free subgroup $G< PSL_2(\mathbb{C})$, hence $\mathbb{H}^3/G$ is a h …
Ian Agol's user avatar
  • 68.9k
25 votes

Elevator pitch for the Virtual Fibering Theorem

I suppose I'm obligated to make a stab at answering this :) First, the virtual fibering question was asked by Thurston: "Does every hyperbolic 3-manifold have a finite-sheeted cover which fibers over …
Martin Sleziak's user avatar
5 votes
Accepted

Knotted concordances of slice links

I think this is likely an unknown question. Namely, the negation of 3) would follow from 1) and 2) if strongly slice links are strongly ribbon (which seems to be open) ribbon disks bounding the unkno …
Ian Agol's user avatar
  • 68.9k
8 votes

Best known Margulis constants?

Results of Culler and Shalen together with tameness, density, etc. imply that there exists a number $V$ such that if $M$ is a hyperbolic 3-manifold of volume $>V$, then the Margulis constant of $M$ is …
Ian Agol's user avatar
  • 68.9k
6 votes

A degree of an arbitrary polynomial knot

Suppose one has a polynomial long knot given as the image of the function $P(t)=(p_1(t),p_2(t),p_3(t)), t\in \mathbb{R}$, where $degree(p_i)\leq d, 1\leq i\leq 3$. Then the crossing number will be bou …
The Amplitwist's user avatar
12 votes
Accepted

Geometrization for 3-manifolds that contain two-sided projective planes

Most 3-manifold topologists tend to hypothesize away 2-sided projective planes. If a 3-manifold contains a 2-sided projective plane, then it must be non-orientable, and the preimage of the projective …
Ian Agol's user avatar
  • 68.9k

1
2 3 4 5
20
15 30 50 per page