Four specifications of a C-element with inputs X, Y and an output Z. a Conventional logic table, where ‘unchanged’ means that the state of the output is the last stable configuration of 1 or 0. b State graph, in which each state denotes a configuration and a transition is caused by the presence of a signal, where * indicates that the signal is excited. c 1-bounded Petri net specifying the Muller C-element. d Timing diagram for the C-element