27 research outputs found
Algebra, coalgebra, and minimization in polynomial differential equations
We consider reasoning and minimization in systems of polynomial ordinary
differential equations (ode's). The ring of multivariate polynomials is
employed as a syntax for denoting system behaviours. We endow this set with a
transition system structure based on the concept of Lie-derivative, thus
inducing a notion of L-bisimulation. We prove that two states (variables) are
L-bisimilar if and only if they correspond to the same solution in the ode's
system. We then characterize L-bisimilarity algebraically, in terms of certain
ideals in the polynomial ring that are invariant under Lie-derivation. This
characterization allows us to develop a complete algorithm, based on building
an ascending chain of ideals, for computing the largest L-bisimulation
containing all valid identities that are instances of a user-specified
template. A specific largest L-bisimulation can be used to build a reduced
system of ode's, equivalent to the original one, but minimal among all those
obtainable by linear aggregation of the original equations. A computationally
less demanding approximate reduction and linearization technique is also
proposed.Comment: 27 pages, extended and revised version of FOSSACS 2017 pape
Modular coinduction up-to for higher-order languages via first-order transition systems
The bisimulation proof method can be enhanced by employing âbisimulations up-toâ techniques. A comprehensive theory of such enhancements has been developed for first-order (i.e., CCS-like) labelled transition systems (LTSs) and bisimilarity, based on abstract fixed-point theory and compatible functions. We transport this theory onto languages whose bisimilarity and LTS go beyond those of first-order models. The approach consists in exhibiting fully abstract translations of the more sophisticated LTSs and bisimilarities onto the first-order ones. This allows us to reuse directly the large corpus of up-to techniques that are available on first-order LTSs. The only ingredient that has to be manually supplied is the compatibility of basic up-to techniques that are specific to the new languages. We investigate the method on the Ï-calculus, the λ-calculus, and a (call-by-value) λ-calculus with references
Modélisation et analyse de systÚmes asynchrones avec CADP
La conception des systÚmes industriels critiques comportant du parallélisme asynchrone nécessite l'utilisation de méthodes formelles, assistées par des outils de vérification adaptés, afin de détecter et corriger les erreurs le plus tÎt possible. Dans ce rapport, nous illustrons l'emploi de la boßte à outils CADP pour la modélisation et la vérification formelle de tels systÚmes, à travers l'exemple d'une unité dédiée au perçage des piÚces métalliques. Nous décrivons en langage LOTOS deux versions différentes de l'unité, régies par un contrÎleur principal séquentiel, respectivement parallÚle. Ensuite, nous effectuons la génération et la minimisation des deux espaces d'états sous-jacents, ainsi que l'inspection visuelle de celui, plus petit, correspondant à la version équipée du contrÎleur séquentiel. Finalement, nous analysons le comportement des deux versions de l'unité de perçage en employant deux méthodes de vérification complémentaires, basées sur les bisimulations (equivalence checking) et les logiques temporelles (model checking)
Utilisation d'un Moteur SMT pour générer des Automates Symboliques - Version étendue
Open pNets are used to model the behaviour of open systems, both synchronousor asynchronous, expressed in various calculi or languages. They are endowed with a symbolicoperational semantics in terms of so-called âOpen Automataâ. This allows us to check properties ofsuch systems in a compositional manner. We implement an algorithm computing these semantics,building predicates expressing the synchronization conditions between the events of the pNet subsystems.Checking such predicates requires symbolic reasoning over first order logics, but alsoover application-specific data. We use the Z3 SMT engine to check satisfiability of the predicates,and prune the open automaton of its unsatisfiable transitions. As an industrial oriented use-case,we use so-called "architectures" for BIP systems, that have been used in the framework of anESA project and to specify the control software of a nanosatellite at the EPFL Space EngineeringCenter. We use pNets to encode a BIP architecture extended with explicit data, and compute itsopen automaton semantics. This automaton may be used to prove behavioural properties; we give2 examples, a safety and a liveness property.Les pNets ouverts sont utilisĂ©s pour modĂ©liser le comportement des systĂšmes ouverts,synchrones ou asynchrones, exprimĂ©e dans divers calculs ou langages de programmation. Ils sontdotĂ©s dâune sĂ©mantique opĂ©rationnelle symbolique en termes dâ«Automata Ouverts». Cela nouspermet de vĂ©rifier les propriĂ©tĂ©s de ces systĂšmes dâune maniĂšre compositionnelle. Nous avonsimplĂ©mentĂ© un algorithme calculant ces sĂ©mantiques, en construisant des prĂ©dicats exprimant lesconditions de synchronisation entre les actions des composants du pNet. La vĂ©rification de telsprĂ©dicats nĂ©cessite un raisonnement symbolique sur les logiques de premier ordre, mais Ă©galementsur des donnĂ©es spĂ©cifiques Ă lâapplication. Nous utilisons le moteur SMT Z3 pour vĂ©rifier lasatisfiabilitĂ© des prĂ©dicats, et ne conserver dans lâautomate ouvert que les transitions satisfiables.Nous illustrons notre approche par un exemple dâinspiration industrielle. Pour cela nouspartons dâ«architectures» de systĂšmes BIP, qui ont Ă©tĂ© utilisĂ©s dans le cadre dâun projet delâAgence Spatiale EuropĂ©enne pour spĂ©cifier le logiciel de contrĂŽle dâun nanosatellite au CentredâingĂ©nierie spatiale de lâEPFL. Nous utilisons les pNets pour encoder une architecture BIPĂ©tendu avec des donnĂ©es explicites, et calculer sa sĂ©mantique en termes dâautomates ouverts.Cet automate peut ĂȘtre utilisĂ© pour prouver des propriĂ©tĂ©s comportementales; nous donnons 2exemples, une propriete de suretĂ© et une de vivacitĂ©
On Bisimilarity and Substitution in Presence of Replication
International audienceWe prove a new congruence result for the pi-calculus: bisimilarity is a congruence in the sub-calculus that does not include restriction nor sum, and features top-level replications. Our proof relies on algebraic properties of replication, and on a new syntactic characterisation of bisimilarity. We obtain this characterisation using a rewriting system rather than a purely equational axiomatisation. We then deduce substitution closure, and hence, congruence. Whether bisimilarity is a congruence when replications are unrestricted remains open
Bisimulation symbolique pour les systÚmes ouverts et paramétrés - Version étendue
Les automates ouverts(OA) sont des modĂšles symboliques et paramĂ©trĂ©s pour les systĂšmes concurrents ouverts. Ici,ouvert dĂ©signe des systĂšmes partiellement spĂ©cifiĂ©s, qui peuvent ĂȘtre instanciĂ©s ou assemblĂ©s pour construire de plus grands systĂšmes. Une propriĂ©tĂ© importante pour de tels systĂšmes est la "compositionnalitĂ©", ce qui signifie que les propriĂ©tĂ©s logiques et les Ă©quivalences peuvent ĂȘtre vĂ©rifiĂ©es localement et seront prĂ©servĂ©es par la composition. Dans des travaux antĂ©rieurs, une notion dâĂ©quivalence nommĂ©e FH-Bisimulationa Ă©tĂ© dĂ©finie pour les automates ouverts et se rĂ©vĂ©lait ĂȘtre une congruence pour leur composition. Mais cette Ă©quivalence a Ă©tĂ© dĂ©finie pour une variante des automates ouverts intrinsĂšquement infinis,ce qui la rend impropre au traitement algorithmique.Nous dĂ©finissons une nouvelle forme dâĂ©quivalence nommĂ©e StrFH-Bisimulation, travaillant sur des codages finis des OA. Nous prouvons que la StrFH-Bisimulation est cohĂ©rente et complĂšte pour la FH-Bisimulation.Nous proposons ensuite deux algorithmes pour vĂ©rifier StrFH-Bisimulation: le premier re-quiert une relation (dĂ©finie par lâutilisateur) entre les Ă©tats de deux OA finis, et vĂ©rifie sâil sâagit dâune strFH-Bisimulation. La seconde prend deux AO finies en entrĂ©e et construit une "StrFH-bisimulation la plus faible" telle que leurs Ă©tats initiaux soient bisimilaires. Nous prouvons que cet algorithme termine lorsque les domaines de donnĂ©es sont finis. Les deux algorithmes utilisent un solveur SMT comme base pour rĂ©soudre les obligations de preuve
CAESAR_SOLVE: A Generic Library for On-the-Fly Resolution of Alternation-Free Boolean Equation Systems
Boolean Equation Systems (BESs) provide a useful framework for modeling various verification problems on finite-state concurrent systems, such as equivalence checking and model checking. These problems can be solved on-the-fly (i.e., without constructing explicitly the state space of the system under analysis) by using a demand-driven construction and resolution of the corresponding BES. In this report, we present a generic software library dedicated to on-the-fly resolution of alternation-free BESs (i.e., without mutually recursive minimal and maximal fixed point equations). Four resolution algorithms are currently provided by the library: algorithms A1 and A2 are general, the latter being optimized to produce small-depth diagnostics, whereas algorithms A3 and A4 are specialized for handling acyclic and disjunctive/conjunctive BESs in a memory-efficient way. The library is developed within the CADP verification toolbox using the generic OPEN/CAESAR environment and is currently used for three purposes: on-the-fly equivalence checking modulo five widely-used equivalence relations, on-the-fly model checking of regular alternation-free mu-calculus, and on-the-fly reduction of state spaces based on tau-confluence
Dualities in modal logic
Categorical dualities are an important tool in the study of (modal) logics. They offer conceptual understanding and enable the transfer of results between the different semantics of a logic. As such, they play a central role in the proofs of completeness theorems, Sahlqvist theorems and Goldblatt-Thomason theorems. A common way to obtain dualities is by extending existing ones. For example, Jonsson-Tarski duality is an extension of Stone duality. A convenient formalism to carry out such extensions is given by the dual categorical notions of algebras and coalgebras. Intuitively, these allow one to isolate the new part of a duality from the existing part. In this thesis we will derive both existing and new dualities via this route, and we show how to use the dualities to investigate logics. However, not all (modal logical) paradigms fit the (co)algebraic perspective. In particular, modal intuitionistic logics do not enjoy a coalgebraic treatment, and there is a general lack of duality results for them. To remedy this, we use a generalisation of both algebras and coalgebras called dialgebras. Guided by the research field of coalgebraic logic, we introduce the framework of dialgebraic logic. We show how a large class of modal intuitionistic logics can be modelled as dialgebraic logics and we prove dualities for them. We use the dialgebraic framework to prove general completeness, Hennessy-Milner, representation and Goldblatt-Thomason theorems, and instantiate this to a wide variety of modal intuitionistic logics. Additionally, we use the dialgebraic perspective to investigate modal extensions of the meet-implication fragment of intuitionistic logic. We instantiate general dialgebraic results, and describe how modal meet-implication logics relate to modal intuitionistic logics
Ătude et implĂ©mentation d'une mĂ©thode de transformation des automates temporisĂ©s en automates Ă Ă©tats finis
Les systĂšmes Ă Ă©vĂ©nements discrets (SED) sont des systĂšmes dont le fonctionnement se traduit par des sĂ©quences d'interactions.Les SED peuvent ĂȘtre dĂ©crits par leurs sĂ©quences possibles d'interactions ou Ă©vĂ©nements. Un SED temps-rĂ©el est un SED dont le bon fonctionnement dĂ©pend non seulement de comment il interagit avec son environnement mais aussi Ă quels moments ces interactions se produisent. Le modĂšle automate temporisĂ© (AT) permet de modĂ©liser convenablement les SED temps-rĂ©el.Les ATs, qui utilisent un modĂšle continu du temps, induisent un espace d'Ă©tats infini pour le systĂšme modĂ©lisĂ©. Le modĂšle d'automates Ă Ă©tats finis (AEF) par contre permet de reprĂ©senter de maniĂšre finie l'espace des Ă©tats d'un SED.Les AEFs se prĂȘtent mieux Ă l'Ă©tude (analyse, test, conception, contrĂŽle...) par des mĂ©thodes formelles des SED. Une approche standard pour l'Ă©tude des SED temps-rĂ©el consiste alors Ă transformer l'AT modĂ©lisant le SED en un AEF Ă©quivalent sur lequel on rĂ©alise l'Ă©tude. Dans ce projet, il s'agissait pour nous d'apporter notre contribution Ă l'Ă©laboration d'une nouvelle mĂ©thode de transformation d'un AT en un AEF Ă©quivalent.--RĂ©sumĂ© abrĂ©gĂ© par UMI