Affiliation: | a Institute of Physics, University of Tokyo, Komaba, Tokyo 153, Japan b Department of Mathematics, North Carolina State University, Raleigh, NC 27695-8205, USA c Department of Mathematical Science, Faculty of Engineering Science, Osaka University, Toyonaka, Osaka 560, Japan d Department of Mathematics and Physics, National Defense Academy, Yokosuka 239, Japan e Department of Physics, Rikkyo University, Nishi-Ikebukuro, Tokyo 171, Japan |