Prof. J. Janas Inst. of Mathematics PAN ul. Sw. Tomasza 30 31-027 Krakow Poland |
Dr. P. Kurasov Dept. of Mathematics Lund Inst. of Technology Box 118, 221 00 Lund Sweden |
Prof. S. Naboko Dept. of Math. Physics St.Petersburg Univ. 198904 St.Petersbrug Russia |