Por Jean-Éric Pin (Institut de Recherche en Informatique Fondamentale, CNRS et University Paris-Diderot).

Abstract: Difference hierarchies were originally introduced by Hausdorff and they play an important role in descriptive set theory. In this lecture, I will review standard techniques on difference hierarchies, mostly due to Hausdorff. These techniques will be illustrated by some decidability results on difference hierarchies based on shuffle ideals and polynomials of group languages.