1. Department of Mathematics and Science Education, Tokyo University of Science, 1-3 Kagurazaka, Shinjuku-ku, Tokyo 162-8601, Japan
2. Department of Mathematics, Tokyo University of Science, 1-3 Kagurazaka, Shinjuku-ku, Tokyo 162-8601, Japan
3. Center for Quantum Spacetime, Sogang University, Seoul 04107, South Korea