Zeng, Q. “Language, Liveness and Fairness Invariant in Decomposition of Petri Net Based on the Index of Place”. INFOCOMP Journal of Computer Science, vol. 5, no. 1, Mar. 2006, pp. 11-18, https://infocomp.dcc.ufla.br/index.php/infocomp/article/view/117.