AN ALGEBRAIC CHARACTERIZATION OF OBSERVATIONAL EQUIVALENCE

We show that observational equivalence can be characterized by saturat ing homomorphisms (with respect to Hennessy-Milner logic), thus bringi ng together results developed independently by Castellani and by Arnol d and Dicky on characterizations of transition system equivalences. We take this opportunity to compare Castellani's abstraction homomorphis ms and Arnold-Dicky's saturating homomorphisms. It turns out that they are very similar notions: their difference in formulation is partly d ue to the fact that abstraction homomorphisms were defined on a restri cted class of transition systems.