  We consider global dynamics of reaction systems as introduced by Ehrenfeucht
and Rozenberg. The dynamics is represented by a directed graph, the so-called
transition graph, and two reaction systems are considered equivalent if their
corresponding transition graphs are isomorphic. We introduce the notion of a
skeleton (a one-out graph) that uniquely defines a directed graph. We provide
the necessary and sufficient conditions for two skeletons to define isomorphic
graphs. This provides a necessary and sufficient condition for two reactions
systems to be equivalent, as well as a characterization of the directed graphs
that correspond to the global dynamics of reaction systems.
