Here is a similarly challenging variant of the firing-line synchronization problem. Consider an arbitrary network of identical M machines, each an FSM with three IC-wire bidirectional ports. Every port of an M module must connect to another port of an M module, although two ports of a single module may also be connected. A sample "firing mob" is diagrammed below
All modules make transitions synchronously with a shared clock. On some clock edge, exactly one module is forced into a trigger state by means of an external input (say, by pressing a button); on some subsequent clock edge, all modules are simultaneously to enter a fure state.