@INPROCEEDINGS{PCVC99,
  author = "V. Valero and D. De Frutos and F. Cuartero",
  title = "{On Non-Decidability of reachability for Time Arcs Petri Nets}",
  booktitle = "Proceedings . of XXth PNPM",
  publisher = "IEEE. Computer Society",
  year = "1999",
}