In: ``Developments in Language Theory II: at the crossroads of mathematics, computer science and biology'', World Scientific, pages 396-405. 1996.
Abstract: Some restrictions on the in- and out-degree of the transitions in Petri nets are imposed, and some hierarchies of Petri net languages are obtained. For lambda-labeled Petri nets, a new normal form is derived. It is called the `super-normal form' of Petri net and it improves the Pelz's normal form, with respect to the interleaving semantics.
Keywords: Petri net languages, interleaving semantics, super-normal form.