In: Petri Net Newsletter No. 50, pages 15-26. April 1996.
Abstract: The paper shows the difficulties to compute state-invariants for Timed Petri nets, working with transition durations under the earliest firing rule. The main result is that we can use the S-invariants of the underlying (untimed) Petri net to generate non-linear state-invariants of the timed net to test the non-reachability of states.