広島大学 00182079 33 1 1 14 2003-03-00 2003-03-00 An umbilical point on a non-real-analytic surface Ando,Naoya Hiroshima University Hiroshima mathematical journal Ando,Naoya Department of Mathematics, Faculty of Science, Kumamoto University, 2-39-1 Kurokami, Kumamoto 860-8555, Japan