1. Text Information Processing Laboratory, Kitami Institute of Technology, Kitami 090-8507, Japan
2. Institute of Middle and Far Eastern Studies, Faculty of International and Political Studies, Jagiellonian University, 30-387 Krakow, Poland
3. Independent Researcher, Sapporo 060-0808, Japan
4. Langauge Media Laboratory, Hokkaido University, Sapporo 060-0808, Japan