Labelled superposition

The work presented in this thesis consists of two parts: The first part presents a formalization of the splitting rule for case analysis in superposition and a proof of its correctness, as well as the integration into splitting of a novel approach to lemma learning, which allows the derivation of non-ground lemmas. The second part deals with the application of hierarchic superposition, and in particular superposition modulo linear arithmetic SUP(LA), to the verification of timed and probabilistic timed systems. It contains the following three main contributions: Firstly, a SUP(LA) decision procedure for reachability in timed automata, which is among the first decision procedures for free first-order logic modulo linear arithmetic; secondly, an automatic induction rule for SUP(LA) based on loop detection, whose application allows a generalization of the decidability result for timed automata to timed automata with unbounded integer variables; and thirdly, a formalism for modelling probabilistic timed systems with first-order background theories, as well as a novel approach for the analysis of such systems based on a reduction to model checking using SUP(LA) proof enumeration.Diese Arbeit besteht aus zwei Teilen: Im ersten Teil wird die Splitting-Regel zur Fallunterscheidung im Superpositionskalkül formalisiert und die Korrektheit der Formalisierung bewiesen. Ausserdem wird die Splitting-Regel mit einem neuartigen Verfahren zum Lernen von Lemmata erweitert, welches das Lernen von nicht-grund Lemmata erlaubt. Der zweite Teil befasst sich mit der Anwendung des hierarchischen Superpositionskalküls, insbesondere von Superposition modulo linearer Arithmetik SUP(LA), zur Verifikation von Echtzeit- und probabilistischen Echtzeitsystemen. Die drei wichtigsten Beiträge in diesem Teil sind: Erstens, ein SUP(LA)-basiertes Entscheidungsverfahren für Timed Automata, welches zu den ersten Entscheidungsverfahren für die hierarchische Kombination der freien Logik erster Stufe mit linear Arithmetik gehört; zweitens, eine Regel zur automatischen Induktion in SUP(LA), die auf der Erkennung von Schleifen basiert, und dank derer das Entscheidbarkeitsresultat für Timed Automata hin zu Timed Automata mit unbeschränkten Integer-Variablen verallgemeinert wird; und drittens, ein Formalismus zur Modellierung probabilistischer Echtzeitsysteme mit Hintergrundtheorien erster Stufe, sowie ein neuartiges Verfahren zur Analyse ebensolcher Systeme, welches auf einer Aufzählung von Erreichbarkeitsbeweisen in SUP(LA) sowie einer Zurückführung auf das Model Checking-Verfahren basiert

Automatic Generation of Invariants for Circular Derivations in {SUP(LA)} 1

The hierarchic combination of linear arithmetic and firstorder logic with free function symbols, FOL(LA), results in a strictly more expressive logic than its two parts. The SUP(LA) calculus can be turned into a decision procedure for interesting fragments of FOL(LA). For example, reachability problems for timed automata can be decided by SUP(LA) using an appropriate translation into FOL(LA). In this paper, we extend the SUP(LA) calculus with an additional inference rule, automatically generating inductive invariants from partial SUP(LA) derivations. The rule enables decidability of more expressive fragments, including reachability for timed automata with unbounded integer variables. We have implemented the rule in the SPASS(LA) theorem prover with promising results, showing that it can considerably speed up proof search and enable termination of saturation for practically relevant problems

A Quantum Game of Life

This research describes a three dimensional quantum cellular automaton (QCA) which can simulate all other 3D QCA. This intrinsically universal QCA belongs to the simplest subclass of QCA: Partitioned QCA (PQCA). PQCA are QCA of a particular form, where incoming information is scattered by a fixed unitary U before being redistributed and rescattered. Our construction is minimal amongst PQCA, having block size 2 x 2 x 2 and cell dimension 2. Signals, wires and gates emerge in an elegant fashion.Comment: 13 pages, 10 figures. Final version, accepted by Journ\'ees Automates Cellulaires (JAC 2010)

Compositional Verification for Timed Systems Based on Automatic Invariant Generation

We propose a method for compositional verification to address the state space explosion problem inherent to model-checking timed systems with a large number of components. The main challenge is to obtain pertinent global timing constraints from the timings in the components alone. To this end, we make use of auxiliary clocks to automatically generate new invariants which capture the constraints induced by the synchronisations between components. The method has been implemented in the RTD-Finder tool and successfully experimented on several benchmarks

Compositional Invariant Generation for Timed Systems

International audienceIn this paper we address the state space explosion problem inherent to model-checking timed systems with a large number of components. The main challenge is to obtain pertinent global timing constraints from the timings in the components alone. To this end, we make use of auxiliary clocks to automatically generate new invariants which capture the constraints induced by the synchronisations between components. The method has been implemented as an extension of the D-Finder tool and successfully experimented on several benchmarks

Rewriting Modulo SMT

Combining symbolic techniques such as: (i) SMT solving, (ii) rewriting modulo theories, and (iii) model checking can enable the analysis of infinite-state systems outside the scope of each such technique. This paper proposes rewriting modulo SMT as a new technique combining the powers of (i)-(iii) and ideally suited to model and analyze infinite-state open systems; that is, systems that interact with a non-deterministic environment. Such systems exhibit both internal non-determinism due to the system, and external non-determinism due to the environment. They are not amenable to finite-state model checking analysis because they typically are infinite-state. By being reducible to standard rewriting using reflective techniques, rewriting modulo SMT can both naturally model and analyze open systems without requiring any changes to rewriting-based reachability analysis techniques for closed systems. This is illustrated by the analysis of a real-time system beyond the scope of timed automata methods

Timed-pNets: a communication behavioural semantic model for distributed systems

International audienceThis paper presents an approach to build a communicationbehavioural semantic model for heterogeneousdistributed systems that include synchronous and asynchronouscommunications. Since each node of such systemhas its own physical clock, it brings the challenges of correctlyspecifying the system time constraints. Based on thelogical clocks proposed by Lamport, and CCSL proposed byAoste team in INRIA, as well as pNets from Oasis teamin INRIA, we develop timed-pNets to model communicationbehaviours for distributed systems. Timed-pNets are treestyle hierarchical structures. Each node is associated with atimed specification which consists of a set of logical clocksand some relations on clocks. The leaves are representedby timed-pLTSs. Non-leaf nodes (called timed-pNets nodes)are synchronisation devices that synchronize the behavioursof subnets (these subnets can be leaves or non-leaf nodes).Both timed-pLTSs and timed-pNets nodes can be translatedto timed specifications. All these notions and methods are illustratedon a simple use-case of car insertion from the areaof intelligent transportation systems (ITS). In the end theTimeSquare tool is used to simulate and check the validityof our model