I would like to improve my "depth of understanding" in 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 of at most twenty pages or a book containing at most one hundred pages. By accessible, I mean a(n almost) self-contained paper for postgraduate students.

Here are some examples which I think are 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 is 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 complementary: I ask about some interesting subjects which are typically not available in these classical references.