SNC 是簡單的且其活動性條件是簡單的。吾人發展一有效率的技術去找出壞的siphons 用於資源共享FMS 之死結預防。由此而產生強於現有的模型。 Any SNC is bounded and its liveness conditions are simple. We develop a new systematic technique to find bad siphons (i.e., not traps) and extend the SNC model to FMS (Flexible Manufacturing System) with resource sharing. The resulting nets are more powerful than existing models in the literature.