Foreword

Abstract

The papers contained in this volume are lectures and seminars presented at the 20th “Universitätswochen für Kernphysik” in Schladming in February 1981. The goal of this school was to review some rapidly developing branches in mathematical physics. Thanks to the generous support provided by the Austrian Federal Ministry of Science and Research, the Styrian Government and other sponsors, it has been possible to keep up with the — by now already traditional — standards of this school. The lecture notes have been reexamined by the authors after the school and are now published in their final form, so that a larger number of physicists may profit from them. Because of necessary limitations in space all details connected with the meeting have been omitted and only brief outlines of the seminars were included. It is a pleasure to thank all the lecturers for their efforts, which made it possible to speed up the publication. Thanks are also due to Mrs. Krenn for the careful typing of the notes.