[{"content":" ","date":"8 May 2026","externalUrl":null,"permalink":"/","section":"About Me","summary":" ","title":"About Me","type":"page"},{"content":"","date":"8 May 2026","externalUrl":null,"permalink":"/tags/continued-fractions/","section":"Tags","summary":"","title":"Continued Fractions","type":"tags"},{"content":"","date":"8 May 2026","externalUrl":null,"permalink":"/tags/decidability/","section":"Tags","summary":"","title":"Decidability","type":"tags"},{"content":"","date":"8 May 2026","externalUrl":null,"permalink":"/tags/decision-problems/","section":"Tags","summary":"","title":"Decision Problems","type":"tags"},{"content":"This course employed both slides and fancy chalk. The lecture notes recreate the chalkboard presentation.\nAbstract: # We will begin with a general survey of decision problems related to the orbits and invariants of linear dynamical systems and how these problems relate to properties of recurrence sequences. This section will focus on principal techniques, open problems, and current challenges in the field. The second part of these lectures will narrow our focus to second-order P-finite sequences. Recall that a sequence is P-finite if it satisfies a linear recurrence relation with polynomial coefficients. We will connect the decision problems for second-order P-finite sequences to the convergence of polynomial continued fractions.\n","date":"8 May 2026","externalUrl":null,"permalink":"/talks/202605warsawsimons/","section":"Slides and Notes","summary":"Mini-course at the Simons Semester: Continued fractions, fractals, ergodic theory and dynamics held at the Institute of Mathematics of the Polish Academy of Sciences","title":"Decision Problems, Recurrence Sequences, and Continued Fractions","type":"talks"},{"content":"","date":"8 May 2026","externalUrl":null,"permalink":"/tags/holonomic-sequences/","section":"Tags","summary":"","title":"Holonomic Sequences","type":"tags"},{"content":"","date":"8 May 2026","externalUrl":null,"permalink":"/tags/minimality-problem/","section":"Tags","summary":"","title":"Minimality Problem","type":"tags"},{"content":"","date":"8 May 2026","externalUrl":null,"permalink":"/tags/p-finite-sequences/","section":"Tags","summary":"","title":"P-Finite Sequences","type":"tags"},{"content":"","date":"8 May 2026","externalUrl":null,"permalink":"/tags/positivity-problem/","section":"Tags","summary":"","title":"Positivity Problem","type":"tags"},{"content":"","date":"8 May 2026","externalUrl":null,"permalink":"/talks/","section":"Slides and Notes","summary":"","title":"Slides and Notes","type":"talks"},{"content":"","date":"8 May 2026","externalUrl":null,"permalink":"/tags/","section":"Tags","summary":"","title":"Tags","type":"tags"},{"content":"","date":"14 January 2026","externalUrl":null,"permalink":"/authors/","section":"Authors","summary":"","title":"Authors","type":"authors"},{"content":"","date":"14 January 2026","externalUrl":null,"permalink":"/tags/determination-problems/","section":"Tags","summary":"","title":"Determination Problems","type":"tags"},{"content":"Slides given in Rennes at POPL 2026.\n","date":"14 January 2026","externalUrl":null,"permalink":"/talks/2026poplrennes/","section":"Slides and Notes","summary":"Presentation slides for POPL 2026","title":"Determination Problems for Orbit Closures and Matrix Groups","type":"talks"},{"content":"","date":"14 January 2026","externalUrl":null,"permalink":"/authors/george/","section":"Authors","summary":"","title":"George","type":"authors"},{"content":"","date":"14 January 2026","externalUrl":null,"permalink":"/tags/linear-loops/","section":"Tags","summary":"","title":"Linear Loops","type":"tags"},{"content":"","date":"14 January 2026","externalUrl":null,"permalink":"/tags/orbit-closures/","section":"Tags","summary":"","title":"Orbit Closures","type":"tags"},{"content":"","date":"7 July 2025","externalUrl":null,"permalink":"/tags/algebraic-methods/","section":"Tags","summary":"","title":"Algebraic Methods","type":"tags"},{"content":"","date":"7 July 2025","externalUrl":null,"permalink":"/tags/invariant-generation/","section":"Tags","summary":"","title":"Invariant Generation","type":"tags"},{"content":"","date":"7 July 2025","externalUrl":null,"permalink":"/tags/invariant-verification/","section":"Tags","summary":"","title":"Invariant Verification","type":"tags"},{"content":"","date":"7 July 2025","externalUrl":null,"permalink":"/tags/loop-invariants/","section":"Tags","summary":"","title":"Loop Invariants","type":"tags"},{"content":" Aim # Reasoning about loops is a fundamental task in program analysis and verification. To this end, loop invariants are an indispensable tool. They help both to establish safety properties (e.g., proofs of non-reachability) and liveness properties (e.g., as supporting invariants in termination proofs). Beyer et al. [VMCAI 2007] go so far as to call the problem of automatic invariant generation \u0026ldquo;the most important task in program verification.\u0026rdquo;\nThere has been a resurgence of interest in computing the polynomial invariants for loops. In one direction, theoretical work has produced complete algorithms that will generate the invariant ideal for abstract classes of loops. In another direction, recent works have produced templates and heuristics aimed at generating some (but not necessarily all) the invariants of more general classes of loops with conditional branching, polynomial assignments, and probabilistic updates.\nThis workshop aims to span the divide between the aforementioned directions and bring together researchers from both communities.\nParticipation # To participate in-person, please register for the workshop through ICALP\u0026rsquo;s registration portal. To participate remotely over Zoom, please contact the organisers for further details.\nSpeakers, Talks, and Slides # (Click on a talk title header to reveal the abstract and slides.)\nAlgebraic invariants of rational linear loops — Rida Ait El Manssour (Oxford) Automatically generating loop invariants is essential for ensuring software correctness, yet it remains a challenging problem in general. In this talk, I will focus on a specific class of programs: branching-free loops with a single linear update. I will introduce a PSPACE algorithm that computes all algebraic relationships that consistently hold among program variables throughout the loop’s execution. Additionally, I will highlight how these results can be applied to verify proposed invariants, and discuss promising directions for extending this approach to loops with multiple linear updates.\nThis is based on a project with George Kenison, Mahsa Shirmohammadi, and Anton Varonka.\nS-unit equations in modules — Ruiwen Dong (Magdalen College, Oxford) Let $M$ be a finitely presented module over a Laurent polynomial ring $R$. We consider S-unit equations over $M$: these are equations of the form $x_1 m_1 + \\cdots + x_K m_K = m_0$, where the coefficients $m_i$ are in $M$ and the variables $x_i$ range over the set of monomials of $R$. When the Laurent polynomial ring $R$ has the base ring $\\mathbb{Z}$, (that is, $R = \\mathbb{Z}[X_1^{\\pm}, \\ldots, X_N^{\\pm}]$), we show that it is undecidable whether a given S-unit equation over a given module $M$ admits a solution. When $R$ has the base ring $\\mathbb{Z}/T\\mathbb{Z}$ for some integer $T \u003e 1$, (that is, $R = (\\mathbb{Z}/T\\mathbb{Z})[X_1^{\\pm}, \\ldots, X_N^{\\pm}]$), we show that the problem of deciding whether a given S-unit equation over a given module $M$ admits a solution is Turing equivalent to solving a system of linear-exponential Diophantine equations over $\\mathbb{Z}$.\nThis talk is based on a paper in SODA'25 as well as ongoing work with Doron Shafrir.\nFinite Rational Matrix Semigroups have at most Exponential Size — Roland Guttenberg (TUM) Weighted Automata or equivalently semigroups of matrices are a model for while loops with linear updates. While it has been shown that the optimal polynomial invariants for matrix semigroups can be computed, the algorithms have prohibitively high complexity. In ongoing work together with Rida Ait El Manssour, Nathan Lhote, Mahsa Shirmohammadi and James Worrell we are attempting to tackle the complexity by giving algorithms for identifying and solving simple subcases.\nThe first such simple but interesting subcase are finite semigroups. While it is known that if a group of n-by-n matrices is finite, then it has size at most 2^n n!, for semigroups the best known bound is double exponential. We reduce this bound to a single exponential and obtain a PSPACE algorithm for deciding finiteness of a given matrix semigroup. Our main tool, which is applicable for any matrix semigroup, is the PTIME computation of an irreducible component decomposition. This can be viewed as a kind of extension of the decomposition of a graph into strongly-connected components.\nSlides: 🗎\nApplications of O-Minimality to Linear Loops — Toghrul Karimov (MPI-SWS) The Termination Problem for linear while loops subsumes, among others, the famous Skolem Problem for linear recurrence sequences, and is consequently known to be decidable only in low dimensions (i.e. the number of program variables). We will discuss how o-minimality of real numbers equipped with arithmetic and exponentiation can be used to prove sweeping decidability results—that do not depend on the dimension—for certain robust variants of the classical decision problems of linear loops. This talk is largely based on the paper \u0026ldquo;Verification of Linear Dynamical Systems via O-Minimality of the Real Numbers.\u0026rdquo; Minimizing Cost Register Automata over a Field — Nathan Lhote (Aix-Marseille University) Weighted automata (WA) are an extension of finite automata that define functions from words to values in a given semiring. An alternative deterministic model, called Cost Register Automata (CRA), was introduced by Alur et al. It enriches deterministic finite automata with a finite number of registers, which store values, updated at each transition using the operations of the semiring. It is known that CRA with register updates defined by linear maps have the same expressiveness as WA. Previous works have studied the register minimization problem: given a function computable by a WA and an integer k, is it possible to realize it using a CRA with at most k registers? In this paper, we solve this problem for CRA over a field with linear register updates, using the notion of linear hull, an algebraic invariant of WA introduced recently by Bell and Smertnig. We then generalise the approach to solve a more challenging problem, that consists in minimizing simultaneously the number of states and that of registers. Last, while the linear hull was recently shown to be computable by Bell and Smertnig, no complexity bounds were given. To fill this gap, we provide two new algorithms to compute invariants of WA. This allows us to show that the register (resp. state-register) minimization problem can be solved in 2-ExpTime (resp. in NExpTime).\nThis is joint work with Yahia Idriss Benalioua and Pierre-Alain Reynier\nAlgebraic tools for computing polynomial loop invariants — Fatemeh Mohammadi (KU Leuven) Loop invariants are properties of a loop program that hold before and after each iteration of the loop. They are often employed to verify programs and ensure that algorithms consistently produce correct results during execution. Consequently, the generation of invariants becomes a crucial task for loops. I specifically focus on polynomial loops, where both the loop conditions and assignments within the loop are expressed as polynomials. Although computing polynomial invariants for general loops is undecidable, efficient algorithms have been developed for certain classes of loops. For instance, when all assignments within a while loop involve linear polynomials, the loop becomes solvable. In this talk, I will discuss the more general case where the polynomials exhibit arbitrary degrees. Applying tools from algebraic geometry, I present two algorithms designed to generate all polynomial invariants for a while loop, up to a specified degree. These algorithms differ based on whether the initial values of the loop variables are given or treated as parameters. This talk is based on joint work with Erdenebayar Bayarmagnai and Rémi Prébet.\nSlides: 🗎\nAlgebraic Closure of Matrix Sets Recognized by 1-VASS — Mahsa Naraghi (Université Paris Cité) We prove that for a 1-VASS $\\mathcal V$, with labels $\\Sigma$ and morphism $f:\\Sigma^* \\to M_d(\\mathbb Q)$, the Zariski closure of $f(L(\\mathcal V))$ is computable. To this end, we adapt Imre Simon’s factorisation trees—originally defined for finite monoids—to the infinite monoid $M_d(\\mathbb Q)$ by replacing idempotent elements with stable matrices. We show, through multilinear algebraic arguments, that every sequence of matrices in $M_d(\\mathbb Q)$ can be realised as the yield of a factorisation tree of height bounded by an explicit function of $d$.\nThis work is in collaboration with Rida Ait El Manssour, Mahsa Shirmohammadi, and James Worrell.\nModern algorithms for one block quantifier elimination over the reals — Mohab Safey El Din (Sorbonne Université, CNRS, LIP6) One block quantifier elimination algorithms take as input a formula which consists of a (universal or existential) quantifier on real variables arising in some input polynomial constraints. These algorithms compute a logically equivalent quantifier-free formula of polynomial constraints. This problem is known to be solvable since Tarski\u0026rsquo;s original work on elementary algebra and geometry.\nQuantifier elimination arises frequently in problems related to algebraic reasoning From a geometric perspective, one-block quantifier elimination computes a description of the projection of the real solution set to polynomial constraints on some affine subspace.\nIn this talk, I will describe a new one block quantifier algorithm which leverages this geometric perspective. This yields new complexity results and practical performances which outperform the current state-of-the-art algorithms on a large family of examples.\nSlides: 🗎\nPolynomial Ideals and Order Ideals — Sylvain Schmitz (Université Paris Cité) There is a well-known connection between polynomial ideals and order ideals, which relates e.g. Hilbert\u0026rsquo;s Basis Theorem and the ascending chain condition on polynomial ideals with Dickson\u0026rsquo;s Lemma and the descending chain condition on order ideals.\nAs an illustration of how this connection can be exploited to use complexity results on order ideals, I\u0026rsquo;ll revisit the results of Benedikt, Duff, Sharad, and Worrell [LICS 2017] on the complexity of the zeroness problem for general and invertible polynomial automata, using recent results obtained with Schütze [ICALP 2024]. As a second illustration, I will point to some open questions regarding the complexity of computing Gröbner bases.\nSlides: 🗎\nRational Loop Synthesis — Anton Varonka (TU Wien) Polynomial (equality) invariants have proven to be helpful in the inductive arguments about loop programs. The class of such invariants enjoys good closure properties and most importantly, allows for a finite representation of the set of all polynomial invariants for a given loop program. Therefore, a question of special theoretical interest concerns the decidability/complexity of finding this representation.\nNotably, small changes in the program model can render the problem of generating all polynomial invariants undecidable. We discuss the landscape and focus on the question “What polynomials can be invariants of simple enough loops?”. In this talk, we consider the model of simple linear loops, where the update of the rational variable vector is given by a single rational matrix. Loops like these are exactly the linear dynamical systems, as known in the linear recurrence sequences community. We further restrict ourselves to the loops that attain infinitely many different vectors.\nIn order to understand the polynomial invariants of simple linear loops, we turn to the problem of loop synthesis from desired polynomial equalities. That is, we ask whether there exists a simple linear loop that has a given polynomial invariant. In this setting, synthesising a loop also means finding a vector of initial values\u0026mdash;no surprise that loop synthesis is as hard as Hilbert\u0026rsquo;s Tenth Problem over the rationals.\nOur results concern the decidability of existence and, in addition, the algorithmic generation of loops from invariants. We will discuss special classes of input polynomials: quadratic equations and conjunctions of pure binomial equalities. Finally, we will introduce a bit-bounded version of loop synthesis\u0026ndash;where the objective is to find a simple linear loop with input entries of a bounded size.\nSlides: 🗎\nSchedule # (All times are CEST/UTC+02:00)\n08:30\u0026ndash;09:00 Registration\n09:00\u0026ndash;10:00 Mohab Safey El Din · Modern algorithms for one block quantifier elimination over the reals 10:00\u0026ndash;10:30 Fatemeh Mohammadi · Algebraic tools for computing polynomial loop invariants 10:30\u0026ndash;11:00 Coffee Break\n11:00\u0026ndash;11:30 Rida Ait El Manssour · Algebraic invariants of rational linear loops 11:30\u0026ndash;12:00 Mahsa Naraghi · Algebraic Closure of Matrix Sets Recognized by 1-VASS 12:00\u0026ndash;12:30 Roland Guttenberg · Finite Rational Matrix Semigroups have at most Exponential Size 12:30\u0026ndash;14:00 Lunch\n14:00\u0026ndash;15:00 Nathan Lhote · Minimizing Cost Register Automata over a Field 15:00\u0026ndash;15:30 Sylvain Schmitz · Polynomial Ideals and Order Ideals 15:30\u0026ndash;16:00 Coffee Break\n16:00\u0026ndash;16:30 Anton Varonka · Rational Loop Synthesis 16:30\u0026ndash;17:00 Ruiwen Dong · S-unit equations in modules 17:00\u0026ndash;17:30 Toghrul Karimov · Applications of O-Minimality to Linear Loops Workshop Ends\nOrganisers # George Kenison (LJMU) Mahsa Shirmohammadi (CNRS, Paris) ","date":"7 July 2025","externalUrl":null,"permalink":"/event/loopinvariants/","section":"Workshops Organised","summary":"Workshop On Loop Invariants and Algebraic Reasoning","title":"Loop Invariants and Algebraic Reasoning","type":"event"},{"content":"","date":"7 July 2025","externalUrl":null,"permalink":"/tags/loops/","section":"Tags","summary":"","title":"Loops","type":"tags"},{"content":"","date":"7 July 2025","externalUrl":null,"permalink":"/tags/workshop/","section":"Tags","summary":"","title":"Workshop","type":"tags"},{"content":"","date":"7 July 2025","externalUrl":null,"permalink":"/event/","section":"Workshops Organised","summary":"","title":"Workshops Organised","type":"event"},{"content":" Autobóz # Autobóz is a yearly week-long invitational research camp on Logic, Automata, and Games.\nIn 2023, Autobóz will take place at the Seminarhaus in the Hessische Staatsdomäne Frankenhausen the week between ICALP and Highlights. Indeed, Autobóz is excited to partnership with Highlights as part of the Highlights Collaborative Research Week.\nWe have solicited expert tutorials on topics as diverse as:\nCircuit Verification using Computer Algebra, Daniela Kaufmann (TU Wien, Austria) On Weak Memory Models in Concurrency, Krishna S (IIT Bombay, India) Decision Problems for Linear Recurrence Sequences, George Kenison (TU Wien, Austria) and Logic and automata for message-passing systems, Marie Fortin (CNRS, France). Organisers # George Kenison (TU Wien) Mahsa Shirmohammadi (CNRS, Paris) Klara Nosan (IRIF, Paris) Acknowledgements # We gratefully acknowledge the financial support of both the CNRS and the ANR via the International Emerging Actions grant (IEA'22) and the VeSyAM grant (ANR-22-CE48-0005), respectively.\n","date":"16 July 2023","externalUrl":null,"permalink":"/event/autoboz2023/","section":"Workshops Organised","summary":"Research camp on Logic, Automata, and Games","title":"Autobóz 2023","type":"event"},{"content":"","date":"16 July 2023","externalUrl":null,"permalink":"/tags/automata/","section":"Tags","summary":"","title":"Automata","type":"tags"},{"content":"","date":"16 July 2023","externalUrl":null,"permalink":"/tags/games/","section":"Tags","summary":"","title":"Games","type":"tags"},{"content":"","date":"16 July 2023","externalUrl":null,"permalink":"/tags/logic/","section":"Tags","summary":"","title":"Logic","type":"tags"},{"content":"","date":"16 July 2023","externalUrl":null,"permalink":"/tags/research/","section":"Tags","summary":"","title":"Research","type":"tags"},{"content":"","date":"10 July 2023","externalUrl":null,"permalink":"/tags/reachability/","section":"Tags","summary":"","title":"Reachability","type":"tags"},{"content":"","date":"10 July 2023","externalUrl":null,"permalink":"/tags/recurrences/","section":"Tags","summary":"","title":"Recurrences","type":"tags"},{"content":" Topic # Recursively defined sequences are foundational objects of study in the computational sciences; they arise naturally in areas such as: the analysis of algorithms, weighted automata, loop termination, and probabilistic models.\nAim # The aim of WORReLL'23 is to bring together researchers from the community and showcase cutting-edge research. The one-day workshop will also celebrate the research contributions of Professor James Worrell (also known as Ben). For context, Ben is giving an invited talk at ICALP this year.\nCoincidentally, the workshop is a few days prior to Ben\u0026rsquo;s birthday. We plan to celebrate with a birthday dinner on Sunday 09th July (the evening before the workshop), so please take this into consideration for planning your travel to Paderborn.\nProfessor James Worrell Participation # To participate in-person, please register for WORReLL'23 through ICALP\u0026rsquo;s registration portal. To participate remotely over Zoom, please contact the organisers for further details.\n#ICALP2023 #Workshops | July 10th Workshop On Reachability, Recurrences, and Loops \u0026#39;23 (WORReLL\u0026#39;23)\n👉Organizers:\n\u0026gt; George Kenison @tu_wien\n\u0026gt; Mahsa Shirmohammadi @IRIF_Paris @univ_paris_cite @INS2I_CNRS pic.twitter.com/tUhXQccIYu\n\u0026mdash; ICALP 2023 (@ICALPconf) March 24, 2023 Speakers, Talks, and Slides # (Click on a talk title for the abstract and slides.)\nOn the Complexity of the Sum of Square Roots Problem — Nikhil Balaji (IIT Delhi) Abstract: Given positive integers $a_1, \\dots, a_n$ and $b_1, \\dots, b_m$, the Sum of Square Roots (SSR) problem checks if $\\sum \\sqrt{a_i} \u003e \\sum \\sqrt{b_j}$. While foundational in Computational Geometry, its complexity is in the Counting Hierarchy, and no simple lower bounds exist. This talk introduces a variant of SSR and presents non-uniform algorithms for it.\nSlides: 🗎\nFrom Quantum Automata to Quaternions and Rational Pairing Functions — Paul Bell (Keele) Abstract: We investigate the undecidability of the injectivity problem for Quantum Finite Automata (QFA), focusing on unique acceptance probability for input words. Using linear algebra and quaternions, we discuss state requirements for undecidability based on real or rational initial states.\nSlides: 🗎\nRecursive Sequences and Numeration — Valérie Berthé (CNRS, Paris) Abstract: This lecture explores linear recurrences through the lens of numeration systems and associated dynamical systems, focusing on the finiteness property (where elements with finite expansion form a ring) and its applications in fractal geometry and number theory.\nSlides: 🗎\nGlobe-Hopping — Dmitry Chistikov (Warwick) Abstract: This talk addresses a geometric puzzle involving maximizing the probability of a randomly moved \u0026ldquo;grasshopper\u0026rdquo; landing back in a set (lawn) of fixed area. We discuss 2D optimal shapes and spherical cases depending on the jump length. Joint work with Goulko, Kent, and Paterson. Twisted Rational Zeros of Linearly Recurrent Sequences — Florian Luca (Witwatersrand) Abstract: We examine the Tribonacci sequence\u0026rsquo;s 2-adic valuations, finding that Marques and Lengyel\u0026rsquo;s conjecture fails for most primes. We prove finiteness of \u0026ldquo;twisted rational zeros\u0026rdquo; in non-degenerate linear recurrences, extending the Skolem–Mahler–Lech theorem. Joint work with Bilu, Nieuwveld, Ouaknine, and Worrell.\nSlides: 🗎\nUniversal Skolem Sets — Joël Ouaknine (MPI-SWS) Abstract: The Skolem Problem determines if a linear recurrence has a zero term. We review a new approach using Universal Skolem Sets—sets of integers for which this problem is decidable—based on joint work with Luca, Maynard, Noubissie, and Worrell.\nSlides: 🗎\nThe Positivity Problem for Recurrent Sequences — Veronika Pillwein (JKU) Abstract: Proving positivity for C-finite sequences is challenging, with decidability only known up to order five. We survey computer algebra methods and algorithmic approaches for this problem. Reachability Problems on Matrices and Maps — Igor Potapov (Liverpool) Abstract: We discuss open computational problems regarding matrix semigroups and their connections to linear recurrence sequences and automata theory. We explore the intersection of symbolic/numerical methods in tackling these matrix reachability challenges. The Membership Problem for Hypergeometric Sequences — Mahsa Shirmohammadi (CNRS, Paris) Abstract: This talk is on the Membership problem for rational-valued hypergeometric sequences. Such sequences $\\\\langle u_n \\\\rangle_{n=0}^{\\infty}$ satisfies a first-order linear recurrence relation with polynomial coefficients; that is, a recurrence of the form $f(n)u_n = g(n)u_{n-1}$ where $f,g \\in \\mathbb{Z}[x]$. The Membership Problem asks, given a hypergeometric sequence $\\\\langle u_n \\\\rangle_{n=0}^{\\infty}$ and a target value $t\\in \\mathbb{Q}$, determine whether $t$ occurs in the sequence. We give hints on recent decidability results of the Membership Problem under the assumption that either (i) $f$ and $g$ have distinct splitting fields, (ii) $f$ and $g$ split totally over $\\mathbb{Q}$, and (iii) $f$ and $g$ are monic polynomials that both split over a quadratic extension of $\\mathbb{Q}$.\nThis talk is based on two papers appearing in ISSAC'22 and ISSAC'23, and are in collaboration with George Kenison, Amaury Pouly, Klara Nosan, and James Worrell.\nSchedule # (All times are UTC+02:00)\n08:00\u0026ndash;09:00 Registration\n09:00\u0026ndash;09:45 Valérie Berthé 09:45\u0026ndash;10:30 Dmitry Chistikov\nCoffee Break\n11:00\u0026ndash;11:45 Mahsa Shirmohammadi 11:45\u0026ndash;12:30 Florian Luca\nLunch\n14:05\u0026ndash;14:25 Veronika Pillwein (Online) 14:25\u0026ndash;14:45 Nikhil Balaji 14:45\u0026ndash;15:30 Paul Bell\nCoffee Break\n16:00\u0026ndash;16:45 Igor Potapov 16:45\u0026ndash;17:30 Joël Ouaknine\nWorkshop Ends. (ICALP food and drinks event begins.)\nOrganisers # George Kenison (TU Wien) Mahsa Shirmohammadi (CNRS, Paris) Acknowledgements # We gratefully acknowledge the financial support of both the CNRS and the ANR via the International Emerging Actions grant (IEA'22) and the VeSyAM grant (ANR-22-CE48-0005), respectively.\n","date":"10 July 2023","externalUrl":null,"permalink":"/event/worrell/","section":"Workshops Organised","summary":"Workshop On Reachability, Recurrences, and Loops","title":"WORReLL","type":"event"},{"content":"","externalUrl":null,"permalink":"/categories/","section":"Categories","summary":"","title":"Categories","type":"categories"},{"content":" Peer-Reviewed papers in conference proceedings # On Word Representations and Embeddings in Complex Matrices. arXiv \u0026#32 (with Paul C. Bell, Reino Niskanen, Igor Potapov, and Pavel Semukhin). In: Proceedings of the International Conference on Developments in Language Theory, DLT 2026.\nThe Threshold Problem for Hypergeometric Sequences with Quadratic Parameters. DOI \u0026#32 In: 51st International Colloquium on Automata, Languages, and Programming, ICALP 2024.\nLinear Loop Synthesis for Quadratic Invariants DOI \u0026#32 (with S. Hitarth, Laura Kovács, and Anton Varonka). In: 41st International Symposium on Theoretical Aspects of Computer Science, STACS 2024.\nFrom Polynomial Invariants to Linear Loops. DOI \u0026#32 (with Laura Kovács and Anton Varonka). In: Proceedings of the International Symposium on Symbolic and Algebraic Computation, ISSAC 2023.\nThe Membership Problem for Hypergeometric Sequences with Quadratic Parameters. DOI \u0026#32 (with Klara Nosan, Mahsa Shirmohammadi, and James Worrell). In: Proceedings of the International Symposium on Symbolic and Algebraic Computation, ISSAC 2023.\nPositivity Problems for Reversible Linear Recurrence Sequences. DOI \u0026#32 (with Joris Nieuwveld, Joël Ouaknine, and James Worrell). In: 50th International Colloquium on Automata, Languages, and Programming, ICALP 2023.\nOn the Skolem Problem for Reversible Sequences DOI \u0026#32 In: International Symposium on Mathematical Foundations of Computer Science, MFCS 2022.\nSolving Invariant Generation for Unsolvable Loops. DOI \u0026#32 (with Daneshvar Amrollahi, Ezio Bartocci, Laura Kovács, Marcel Moosbrugger, and Miroslav Stankovič). In Static Analysis: 29th International Symposium, SAS 2022.\nOn Positivity and Minimality for Second-Order Holonomic Sequences. DOI \u0026#32 (with Oleksiy Klurman, Engel Lefaucheux, Florian Luca, Pieter Moree, Joël Ouaknine, Markus A. Whiteland, and James Worrell). In: International Symposium on Mathematical Foundations of Computer Science, MFCS 2021.\nOn the Skolem Problem and Prime Powers. DOI \u0026#32 (with Richard Lipton, Joël Ouaknine, and James Worrell). In: Proceedings of the International Symposium on Symbolic and Algebraic Computation, ISSAC 2020.\nPeer-reviewed articles in journals # Determination Problems for Orbit Closures and Matrix Groups. DOI \u0026#32 (with Rida Ait El Manssour, Mahsa Shirmohammadi, Anton Varonka, and James Worrell). In: Proc. ACM Program. Lang., 10 POPL, pp. 1615\u0026ndash;1640.\nSimple Linear Loops: Algebraic Invariants and Applications. DOI \u0026#32 (with Rida Ait El Manssour, Mahsa Shirmohammadi, and Anton Varonka). In: Proc. ACM Program. Lang., 9 POPL, pp. 745\u0026ndash;771.\n(Un)Solvable loop analysis. DOI \u0026#32 (with Daneshvar Amrollahi, Ezio Bartocci, Laura Kovács, Marcel Moosbrugger, and Miroslav Stankovič). In: Formal Methods in System Design, 2024.\nStatistics in conjugacy classes in free groups. DOI \u0026#32 (with Richard Sharp). In: Geometriae Dedicata 198.1, pp. 57\u0026ndash;70.\nOrbit counting in conjugacy classes for free groups acting on trees. DOI \u0026#32 (with Richard Sharp). In: Journal of Topology and Analysis 9.4, pp. 631\u0026ndash;647.\nPreprints # On the Positivity Problem for second-order holonomic sequences. (with Oleksiy Klurman, Engel Lefaucheux, Florian Luca, Pieter Moree, Joël Ouaknine, Emre Sertöz, Markus A. Whiteland, and James Worrell).\nOn the growth of hypergeometric sequences. arXiv \u0026#32 (with Jakub Konieczny, Florian Luca, Andrew Scoones, Mahsa Shirmohammadi, and James Worrell).\n","externalUrl":null,"permalink":"/publications/","section":"About Me","summary":"Research papers, publications, and preprints","title":"Publications and Preprints","type":"page"},{"content":"","externalUrl":null,"permalink":"/series/","section":"Series","summary":"","title":"Series","type":"series"}]