Vasily A. Dolgushev, Temple University
Grothendieck's child's drawings (a.k.a. dessins d'enfant) connected topology to number theory in a fascinating way. In my first talk, I will present several equivalent definitions of a child's drawing. You will see permutation pairs, bipartite ribbon graphs and finite index subgroups of the free group on two generators. If time permits, I will start talking about Belyi pairs. The absolute Galois group of rational numbers acts on child's drawings and Belyi pairs allow us to introduce this action.