Under the name of ideal circuit network, it is easy to make us understand that digital circuits are independent of the inner status and their outputs just only depend on the inputs. They are time constants and therefore Boolean algebra is a special suitable means of describing. In fact propagation delay time of circuit system should be in thought firstly in designing circuit network. In that case Boolean algebra does not seems to be fully suitable for describing actual circuit systems. Furthermore, Boolean algebra cannot help to locate and repair hazard errors in a circuit thoroughly when the.