@Article{BT04,
  author = 	 {Roberto Barbuti and Luca Tesei},
  title = 	 {Timed Automata with Urgent Transitions},
  journal = 	 {Acta Informatica},
  volume =       {40},
  number =       {5},
  pages =        {317--347},
  year = 	 {2004},
  note =         {Springer, Berlin}
}