Matthias Jantzen.
On the hierarchy of Petri net languages.
R.A.I.R.O. Informatique théorique/Theoretical Informatics,
13(1):19-30, 1979.
@article{Jantzen79, Author = {Jantzen, Matthias}, Journal = {R.A.I.R.O. Informatique th{\'e}orique/Theoretical Informatics}, Number = 1, Pages = {19--30}, Title = {On the hierarchy of {Petri} net languages}, Volume = 13, Year = 1979 }