Affiliation: | (1) Department of Mathematics, Ohio State University, 231 W. 18 Avenue, Columbus, OH 43210–1174, USA (e-mail: silver@math.ohio-state.edu) , US;(2) Department of Mathematics, Pennsylvania State University, University Park, PA 16802, USA (e-mail: zarhin@math.psu.edu) , US;(3) Institute for Mathematical Problems in Biology, Russian Academy of Sciences, Pushchino, Moscow Region, 142292, Russia , RU |