On Confluent Semi-commutations: Decidability and Complexity Results

Decidability and Complexity Results for Security Protocols

Security protocols are prescribed sequences of interactions between entities designed to provide various security services across distributed systems. Security protocols are often wrong due to the extremely subtle properties they are supposed to ensure. Deciding whether or not a security protocol assures secrecy is one of the main challenge in this area. In this paper we survey the most importa...

Some Decidability Results on Grammatical Inference and Complexity

The grammatical inference problem is easy to state: One must choose, on the basis of a finite set of symbol strings, a grammar for the language of which the given set is a sample. Precisely the same problem arises in trying to choose a model (theory, function, etc.) to explain a collection of sample data. This is one of the most important information processing problems known and it is surprisi...

Decidability and Complexity Results for Timed Automata and Semi-linear Hybrid Automata

We define a new class of hybrid automata for which reachability is decidable—a proper superclass of the initialized rectangular hybrid automata—by taking parallel compositions of simple components. Attempting to generalize, we encounter timed automata with algebraic constants. We show that reachability is undecidable for these algebraic timed automata by simulating two-counter Minsky machines. ...

Rewriting, Möbius Functions and Semi-Commutations

Closure of regular languages under semi-commutations

The closure of a regular language under a [partial, semi-] commutation I has been extensively studied. We present new advances on two problems of this area: (1) When is the closure of a regular language under [partial, semi-] commutation still regular? (2) Are there any robust classes of languages closed under [partial, semi-] commutation? We show that the class Pol(G) of polynomials of group l...