Your favorite papers on geometric group theory

I would like to improve my culture on geometric group theory, so I am interested in short and accessible papers on subjects related to this field but which are not always available in the classical references.

To make my question more precise: By short, I mean a research paper about twenty pages or a book containing at most one hundred pages. By accessible, I mean a(n almost) self-contained paper for postgraduate students.

Below are some examples I think they should be suitable:

• Topology of finite graphs, Stallings (15 pages). One of my favorite papers. Stallings shows how to apply covering spaces to finite graphs in order to prove several non trivial properties of free groups.

• Topological methods in group theory, Scott and Wall (about 60 pages). The authors proves several classical results of geometric group theory (Stallings' ends theorem, Grushko's and Kurosh's theorems, Bass-Serre theory) using the formalism of graphs of spaces.

• Subgroups of surface groups are almost geometric, Scott (12 pages). Peter Scott proves that surface groups are LERF by using hyperbolic geometry.

I hope my question will turn out to be precise enough to be of interest.

EDIT: I don't think my question is a duplicate of Introductory text on geometric group theory?. Rather, I see it as a complement: I ask about some interesting subjects which are typically not available into these classical references.

• Community wiki? – joro Jul 8 '15 at 12:54
• Similar to mathoverflow.net/questions/3858/… – Tom Copeland Jul 8 '15 at 14:16
• You already mentioned three of my favourites! – HJRW Jul 8 '15 at 21:10
• I hope the question will be closed and remain closed as primarily opinion-based, especially insofar as it potentially means advertising contemporary articles, and given some kind of ranking (in terms of the number of upvotes) of these papers. – YCor Jul 9 '15 at 14:03
• Note that the poster is not asking for the "best" papers, but rather for suggestions of "favorite" papers. I'm very interested in hearing what the experts have to say! – Sam Nead Jul 25 '15 at 21:41

• Maybe I am missing something, but I find the first assertion of the second paragraph suspicious. I cannot insert a picture in a comment, but the word $b_1^2a_1b_1^{-1}b_2^{-1}$ in $$\langle a_1,a_2,b_1,b_2 \mid [a_1,b_1][a_2,b_2]=1 \rangle$$ seems to be representable as a non singular loop whereas it is neither a standard generator nor a product of commutators of standard generators. – Seirios Jul 28 '15 at 12:38