**11**

votes

**1**answer

795 views

### Topological HNN extensions

First, let me recall what an abstract HNN extension is. Let $G$ be an abstract group, $A, B < G$ be subgroups of $G$ and $\phi : A \to B$ be an isomorphisms. Then there is a group $H$ and an ...

**1**

vote

**1**answer

215 views

### blowing up the graphs

I heard the phrase from many mathematician using in the colloquials. I heard algebraic geometer using it. I was never bother about it until one of my professor responded to one my question as follows:
...

**5**

votes

**1**answer

250 views

### Connections between properties of a group and local symmetries of its Cayley graph

Hi everyone,
Let $\Gamma$ be a finitly generated group.
Does someone know of a connection between properties of $\Gamma$ to local symmetries of its Cayley graph?
More specificly, what can one learn ...

**4**

votes

**2**answers

390 views

### HNN extensions which are free products

which HNN-extensions are free products? this question is related with another still unsolved about Nielsen-Thruston-reducibility and connected-sum-irreducibility of 3d-torus- bundles...

**3**

votes

**1**answer

314 views

### How do Dehn functions of special linear and mapping class groups behave?

Hi,
I apologize for the basic questions. I am looking for good references on the following problems:
1) What is known about the Dehn function of $SL_n(\mathbb{Z})$?
2) What is known about the Dehn ...

**23**

votes

**9**answers

5k views

### Introductory text on geometric group theory?

Can someone indicate me a good introductory text on geometric group theory?