Institution: | (1) Mathematical Institute, Pf. 127, 1364 Budapest, Hungary;(2) Department of Mathematics, Yale University, 06520 New Haven, CT, U. S. A.;(3) Department of Computer Science, Eötvös University, Múzeum krt. 6-8, 1088 Budapest, Hungary;(4) Princeton University, 08544 Princeton, NJ, U. S. A. |