Zhijun Ding Changjun Jiang MengChu Zhou Deadlock Checking for One-Place Unbounded Petri Nets Based on Modified Reachability Trees. 881-883 2008 38 IEEE Transactions on Systems, Man, and Cybernetics, Part B 3 http://dx.doi.org/10.1109/TSMCB.2008.917177 db/journals/tsmc/tsmcb38.html#DingJZ08