This volume represents the proceedings of a NATO Advanced Study
Institute held at Noto, Sicily June 8-19, 1987. The director was
Giovanni Gallavotti, Roma, with co-directors Marcello Anile, Catania and
P. F. Zweifel, Virginia Tech. Other members of the scientific organizing
committee included Mitchell Feigenbaum, Rockefeller University and David
Ruelle, IHES. The attendance at the school consisted of 23 invited
speakers and approximately 80 "students", the term student being in
quotation marks because many of them were of post-doctoral or even
professorial status, although there were also a goodly number of actual
graduate students in attendance also. Because of the disparate
background of these "students", it was felt advisable to include at the
conference special tutorials each afternoon, in which the contents of
the morning's lectures were reviewed and clarified as necessary. These
tutorials, organized by Gallavotti, involved various of the speakers,
organizers, and other senior members of the school, and contributed in
no little way to the overall success of the school. The organizers of
the school would like to take this opportunity to thank all of those who
assisted in these sessions, and to assure them that the results were
definitely worth the effort. Also contributing to the success of the
school were a number of contributed papers, presented during the course
of the afternoon tutorials. Three of those papers are included in these
proceedings; they are the papers of DiFrancesco; Gallimbeni, Miari and
Sertorio (presented by Sertorio); and Vittot.