Robust parametric reachability for timed automata

We review the known decidability and undecidability results for reachability in parametric timed automata. Then, we present a new proof of undecidability in dense time for open timed automata that avoids equalities in clock constraints. Our result shows that the undecidability of parametric timed automata does not follow from their ability to specify punctual constraints in a dense time domain.