Institution: | Department of Mathematics, Hokkaido University Sapporo 060-0810, Japan izumiya{at}math.sci.hokudai.ac.jp, takahashi{at}math.sci.hokudai.ac.jp
Department of Mathematics, Northeast Normal University Changchun 130024, China northlcd{at}public.cc.jl.cn, pei{at}math.sci.hokudai.ac.jp
Departament de Geometría i Topología, Universitat de València 46100 Burjassot (València), Spain carmen.romero{at}post.uv.es |