Reference:

J. Esparza. Petri nets, commutative context-free grammars, and basic parallel processes. In B. Reichel, editor, Proceedings of FCT '95, number 965 in Lecture Notes in Computer Science, pages 221–232, 1995.

Suggested BibTeX entry:

@inproceedings{Esp95,
    author = {J. Esparza},
    booktitle = {Proceedings of FCT '95},
    editor = {B.~Reichel},
    number = {965},
    pages = {221--232},
    series = {Lecture Notes in Computer Science},
    title = {Petri Nets, Commutative Context-Free Grammars, and Basic Parallel Processes},
    year = {1995}
}