Affiliation: | (1) Mathematics 253-37, Caltech, Pasadena, CA 91125, USA;(2) Institute for Information Transmission Problems, Moscow, Russia;(3) Institut Fourier, 100 Rue des maths, 38402 Saint Martin d’Heres, France;(4) Present address: Department of Mathematics, University of California at Davis, One Shields Ave., Davis, CA 95616, USA |