Launching LMF - the Formal Methods Laboratory

The Laboratoire Méthodes Formelles (LMF) was founded on 1 January 2021 as a joint research centre of University Paris-Saclay, CNRS, ENS Paris-Saclay, Inria, and CentraleSupélec with a main focus on formal methods. The new laboratory combines the expertise of about 100 members from the former Laboratoire Spécification et Vérification (LSV) and the VALS team of Laboratoire de Recherche en Informatique (LRI).

In our mission to enlighten the digital world through Mathematical Logic, we rely on formal methods as a tool to analyse, model, and reason about computing systems, such as computer programs, security protocols, and hardware designs. Our research targets a wide range of computational paradigms, from classical to emerging ones such as biological and quantum computing.

LMF is structured around three hubs: Proofs and Models, which lie at the heart of our historical background, and Interactions, that is aimed at fostering cross-fertilisation between formal methods and other domains in computing science and beyond.

The Skolem Landscape

Speaker: Joël Ouaknine, Max Planck Institute for Software Systems, Saarbrücken, Germany

Tuesday Dec 13 2022, 14:00, Room 1Z56

Abstract: The Skolem Problem asks how to determine algorithmically whether a given linear recurrence sequence (such as the Fibonacci numbers) has a zero. It is a central question in dynamical systems and number theory, and has many connections to other branches of mathematics and computer science. Unfortunately, the decidability of the Skolem Problem has been open for nearly a century! In this talk, I will present a survey of what is known on this problem and related questions, including recent and ongoing developments.

Best Process-Mining Dissertation Award for Mathilde Boltenhagen

Mathilde Boltenhagen

Mathilde Boltenhagen received the Best Process Mining PhD Dissertation Award 2022 during the Fourth International Conference on Process Mining (ICPM 2022) for her thesis entitled "Process Instance Clustering based on Conformance Checking Artefacts".

The Best Process Mining PhD Dissertation Award distinguishes theses that contributed to advancing the state of the art in the foundations, engineering, and on-field application of process mining techniques. In this context, the term "process mining" has to be understood in a broad sense: using event data produced during the execution of business, software, or system processes, in order to extract fact-based knowledge and insights on such processes and manage future processes in innovative ways.

Mathilde's thesis contributes to several aspects of conformance checking. It provides a framework and tools to partition log-traces of a process into clusters that use partial-order traces as centroids to take concurrency into account. In her work, Mathilde refined the notion of anti-alignments as a measure for the precision of process model, and she implemented the first efficient approximation of anti-alignments.

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PhD Defence: Amrita Suresh

Formal Verification of Communicating Automata
by Amrita Suresh
Monday 12 December 2022 at 2pm
Room 1Z18, ENS Paris-Saclay and online

Amrita Suresh

Abstract: Distributed systems involve processes that run independently and communicate asynchronously. While they capture a wide range of use cases and are hence, ubiquitous in our world, it is also particularly difficult to ensure their correctness.

In this thesis, we model such systems using mathematical and logical formulation, and try to verify them algorithmically. In particular, we focus on FIFO (First-In First-Out) machines, with one or more finite-state machines communicating via unbounded reliable FIFO buffers. Read more...

PhD Defence: Mathieu Hilaire

Parity games and reachability in infinite-state systems with parameters
by Mathieu Hilaire
Thursday 13 December 2022 at 9am
Room 1Z71, ENS Paris-Saclay and online

Abstract: The most standard model checking approaches are limited to verifying concrete specifications, such as “can we reach a configuration with more than 10 time units elapsing ?”. Nevertheless, for certain computer programs, like embedded systems, the constraints depend on the environment. Thus arises the need for parametric specifications, such as “can we reach a configuration with more than p time units elapsing ?” where p is a parameter which takes values in the non-negative integers.

In this thesis, we study parametric pushdown, counter and timed automata and extensions thereof. In addition to expressing concrete constraints (on the stack, on the counter or on clocks), these can employ parametric constraints. The reachability problem for a parametric automaton asks for the existence of an assignment of the parameters such that there exists an accepting run in the underlying concrete automaton. In addition to the reachability problem, we consider parametric parity games, two player games where players alternate choosing assignments for each parameters, then alternate moving a token along the configurations of the concrete automaton resulting from their choice of parameter assignment. We consider the problem of deciding which player has a winning strategy.

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PhD Defence: Glen Mével

Cosmo: a concurrent separation logic for the weak memory of Multicore OCaml
by Glen Mével
Wednesday 14 December 2022 at 2pm
Inria Paris,. 2 rue Simone Iff, Paris, Salle Lions 1, and online

Abstract: Multicore OCaml extends OCaml with support for shared-memory concurrency. It is equipped with a weak memory model, for which an operational semantics has been published. This begs the question: what reasoning rules can one rely upon while writing or verifying Multicore OCaml code?

To answer it, we instantiate Iris, a modern descendant of Concurrent Separation Logic, for Multicore OCaml. This yields a low-level program logic whose reasoning rules expose the details of the memory model. On top of it, we build a higher-level logic, Cosmo, which trades off some expressive power in return for a simple set of reasoning rules that allow accessing non-atomic locations in a data-race-free manner, exploiting the sequentially-consistent behavior of atomic locations, and exploiting the release/acquire behavior of atomic locations. Cosmo allows both low-level reasoning, where the details of the Multicore OCaml memory model are apparent, and high-level reasoning, which is independent of this memory model.

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Philippe Schnoebelen receives LICS 2022 Test-of-Time Award

Philippe Schnoebelen

Philippe Schnoebelen receives the LICS Test-of-Time Award 2022 for the article Temporal Logic with Forgettable Past co-authored with François Laroussinie (Université Paris-Cité) and Nicolas Markey (IRISA, CNRS). At the time of the writing of the article in 2002, the three authors were members of the same laboratory LSV which integrated the LMF in 2021.

The LICS - Logic in Computer Science conference is the most prestigious annual forum on theoretical and practical topics in computer science related to logic in a broad sense. The LICS Test-of-Time Award award recognizes a small number of papers from the LICS proceedings over the past 20 years (i.e., the paper in question dates from LICS 2002 and was considered this year) that have best stood the "test of time." In selecting these papers, the award committee considers the influence they have had since their publication; due to the fundamental nature of LICS work, the impact is often not felt immediately, hence the 20-year perspective.

Lasting impact on the foundations of automatic verification

According to the awarding jury, "This extraordinarily clear and elegant paper provides well-motivated and complete characterizations of succinctness and complexity of linear temporal logic with past operators and with forgettable past. It has contributed to spur a vibrant research program on logics and automata over infinite alphabets, from hardness results to the translations of logical formulas into alternating register automata, along with the attendant powerful algorithmic consequences for model checking. It has also strongly influenced the development of the field of nominal computation, and it is no exaggeration to state that the present paper has tangibly led to a number of invited talks, Dagstuhl-type workshops, research grants, academic positions, and prizes, and continues to have an ongoing and lasting impact in the areas of automata theory and the foundations of automated verification."

The award will be presented at the conference awards session LICS 2022 organized from August 2 to 5 in the framework of FLOC 2022 -- Federated Logic Conference in Haifa, Israel.