Affiliation: | (1) Universität Jena, Sekt. Math., Universitäts-Hochhaus 17.OG, DDR-6900 Jena;(2) Dept. of Math., Moscow University, Moscow, USSR;(3) Steklov Math. Institute, 42 Vavilova, 117966 GSP-1 Moscow, USSR;(4) Dept. of Math., Moscow University, 117234 Moscow, USSR |