Wintersemester 2016/2017 :
Algebraic Geometry I

Courses: Tuesday and Thursday 10:00-12:00 in Room B 047 .

Exercises classes TBA ( Olivier Haution).

Exercises sheets

Trees, Amalgam, SL2

Fr 10-12 Uhr im B 040. This is a mathematical seminar ment for master students.

The aim of this seminar is to give an introduction to combinatorial groups theory in the following sense: given a group G acting on a combinatorial graph, what can we say on the structure of G if we know for instance the structure of each of the isotropy subgroups of the action of G at each vertex of the graph ? We will emphasize the case of actions of groups on ``trees" and will give several applications. For instance any subgroup of a free group is a free group. Other arithmetical applications will involve the group SL2 acting on ``its" tree that will be introduced in the second part of the seminar.

Main reference:
Arbres, Amalgames, SL2, by J.-P. Serre, Astérisque 1977, also available in english:

Trees, by J.-P. Serre, Springer.

Schedule of the talks.

Previous semesters .