Invariant property preserving extensions of elementary Petri nets

We deene an extension of an elementary Petri net and give a suucient criterion for the preservation of invariant properties. Properties of a net are described by propositional temporal formulas. An elementary Petri net is an extension of another net if the smaller net can be embedded into the larger one by an injective function that maps places on places and transitions on transitions. It is shown that every extension preserves the static properties of the net, viz. the properties expressable in rst order propositional logic. The criterion for the preservation of invariant properties is that the embedding function preserves the pre-and postset of places. That means that the ow relation of the smaller net is preserved and furthermore that only the image of a transition can have a larger pre-or postset in the extension than its soure in the original net.