Osamu Katai Katsushi Minamizono Takayuki Shiose Hiroshi Kawakami System design of "Ba"-like stages for improvisational acts via Leibnizian space-time and Peirce's existential graph concepts. 101-112 2007 22 AI Soc. 2 http://dx.doi.org/10.1007/s00146-007-0125-2 db/journals/ais/ais22.html#KataiMSK07