Institution: | (1) Department of Mathematical Sciences, University of Montana, Missoula, MT 59812-1032, USA (e-mail: ma_blc@ selway.umt.edu) , US;(2) Department of Mathematics, Kiev University, Kiev, 252617, Ukraine , UA;(3) Department of Mathematics, St. Lawrence University, Canton, NY 13617, USA (e-mail: dmel@ slumus.bitnet), US |