Institution: | (1) Department of Mathematics, University of Helsinki, Hallituskatu 15, SF-00100 Helsinki, Finland;(2) Department of Mathematical Sciences, University of Trondheim, NTH, N-7034 Trondheim, Norway;(3) Department of Mathematics, University of Jyväskylä, P.O. Box 35, SF-40351 Jyväskylä, Finland;(4) Department of Mathematics and Statistics, University of Trondheim, AVH, N-7055 Dragvoll, Norway |