Institution: | Institute of Physics, Czechoslovak Acadamy of Sciences, 180 40 Prague 8, Czechoslovakia;Department of Mathematics and Statistics, University of New Mexico, Albuquerque, New Mexico 87131 U.S.A.;Instituto de Investigaciones en Matemáticas Aplicadas y en Sistemas (IIMAS), Universidad Autónoma de México, Apdo. Postal 20-726, 01000 México D.F., Mexico |