1. Give examples of firing sequences for the net of Figure 5.21(a). 2. Describe some of the systems previously described by FSMs by means of PNs. and com-pare the different specifications. 3. Use the foregoing PN extension to describe a message dispatcher that works along the following lines: The dispatcher receives messages from two different channels and then checks the parity of each message. If the parity is wrong, it sends a “nack” (negative acknowledgment) through a reply channel (there is one such channel for each input channel); if the parity is right, it places the received message into a buffer. The buffer may store 10 messages. When the buffer is full, the dispatcher sends the whole contents of the buffer to a processing unit through another channel. No message can be placed into a full buffer.