On liveness preservation by composition of nets via a set of places

In this article, we define classes of Petri nets for which the composition via a set of places preserves liveness. The new notion on which the definition of these classes is based is F-monotonicity. F-monotonicity is a property which refines liveness monotonicity. F-robust nets are defined as nets which are insensitive to some modification of a weighted amount of tokens (marking of places P). A net which can be composed with an F-robust net on P, and which respects the degree of non-sensitivity of the F-robust net is said to be a non-disturbing net with regard to the F-robust net. Nets for which Commoner's property is a necessary and sufficient condition of liveness are shown to be F-robust. Nets with output places are also F-robust nets. The composition of an F-robust net with a non-disturbing net is shown to preserve liveness. F-strong nets constitute another class of nets that we can compose while preserving liveness. State machines are F-strong nets.