Jianan Li Ichiro Suzuki Masafumi Yamashita A New Structural Induction Theorem for Rings of Temporal Petri Nets. 115-126 http://www.computer.org/tse/ts1994/e0115abs.htm 1994 20 IEEE Trans. Software Eng. 2 db/journals/tse/tse20.html#LiSY94