On the occasion of bis sixtieth birthday, we dedicate this volume to Jan Wo- leriski-s-our teacher, our colleague, our friend. Both of us are particularly indebted to Jan not only with regards to profes- sional matters, but some private ones as well. Hence, we hope that he forgives us an occasional lapse into fondness and affection. That said, may the list of bis personalmerits remain shrouded in mystery; rather than unveil them, we open here by appraising Jan's presence from a broader perspective. Tonote that Jan was not always a part of our lives would not evoke surprise. However, to...