@inproceedings{DLT-1995-TipleaE,
	author        = "Ferucio Laurentiu Tiplea and Cristian Ene",
	booktitle     = "{Proceedings of the Second International Conference on Developments in Language Theory: At the Crossroads of Mathematics, Computer Science and Biology}",
	isbn          = "981-02-2682-9",
	pages         = "396--405",
	publisher     = "{World Scientific}",
	title         = "{Hierarchies of Petri Net Languages and a Super-Normal Form}",
	year          = 1995,
}