@Article{	  bdgp98,
  author	= "Beatrice B\'erard and Volker Diekert and Paul Gastin and
		  Antoine Petit",
  journal	= "Fundamenta Informaticae",
  pages		= "145--182",
  title		= "Characterization of the Expressive Power of Silent
		  Transitions in Timed Automata",
  volume	= "36",
  year		= "1998",
  doi		= "10.3233/FI-1998-36233"
}