Tight Upper Bounds for Streett and Parity Complementation

This paper describes some general results about hierarchies of undecidable problems in automata theory, and studies how properties of sets accepted by automata change from decidable to undecidable problems as the memory capacity of the automaton is increased.

The complementation problem for nondeterministic word automata has numerous applications in formal verification. In particular, the language-containment problem, to which many verification problems is reduced, involves complementation. For automata on finite words, which correspond to safety properties, complementation involves determinization. The 2n blow-up that is caused by the subset construction is justified by a tight lower bound. For Büchi automata on infinite words, which are required for the modeling of liveness properties, optimal complementation constructions are quite complicated, as the subset construction is not sufficient. From a theoretical point of view, the problem is considered solved since 1988, when Safra came up with a determinization construction for Büchi automata, leading to a 2O(nlogn) complementation construction, and Michel came up with a matching lower bound. A careful analysis, however, of the exact blow-up in Safra’s and Michel’s bounds reveals an exponential gap in the constants hiding in the O() notations: while the upper bound on the number of states in Safra’s complementary automaton is n 2n, Michel’s lower bound involves only an n! blow up, which is roughly (n/e)n. The exponential gap exists also in more recent complementation constructions. In particular, the upper bound on the number of states in the complementation construction in [KV01], which avoids determinization, is (6n)n. This is in contrast with the case of automata on finite words, where the upper and lower bounds coincides. In this work we describe an improved complementation construction for nondeterministic Büchi automata and analyze its complexity. We show that the new construction results in an automaton with at most (1.06n)n states. While this leaves the problem about the exact blow up open, the gap is now exponentially smaller. From a practical point of view, our solution enjoys the simplicity of [KV01], and results in much smaller automata.

The complementation problem for nondeterministic word automata has numerous applications in formal verification. In particular, the language-containment problem, to which many verification problems is reduced, involves complementation. For automata on finite words, which correspond to safety properties, complementation involves determinization. The 2n blow-up that is caused by the subset construction is justified by a tight lower bound. For Büchi automata on infinite words, which are required for the modeling of liveness properties, optimal complementation constructions are quite complicated, as the subset construction is not sufficient. From a theoretical point of view, the problem is considered solved since 1988, when Safra came up with a determinization construction for Büchi automata, leading to a 2O(n log n) complementation construction, and Michel came up with a matching lower bound. A careful analysis, however, of the exact blow-up in Safra's and Michel's bounds reveals an exponential gap in the constants hiding in the O( ) notations: while the upper bound on the number of states in Safra's complementary automaton is n2n, Michel's lower bound involves only an n! blow up, which is roughly (n/e)n. The exponential gap exists also in more recent complementation constructions. In particular, the upper bound on the number of states in the complementation construction of Kupferman and Vardi, which avoids determinization, is (6n)n. This is in contrast with the case of automata on finite words, where the upper and lower bounds coincides. In this work we describe an improved complementation construction for nondeterministic Büchi automata and analyze its complexity. We show that the new construction results in an automaton with at most (0.96n)n states. While this leaves the problem about the exact blow up open, the gap is now exponentially smaller. From a practical point of view, our solution enjoys the simplicity of the construction of Kupferman and Vardi, and results in much smaller automata.

Mutation analysis is a popular test assessment method. It relies on the mutation score, which indicates how many mutants are revealed by a test suite. Yet, there are mutants whose behaviour is equivalent to the original system, wasting analysis resources and preventing the satisfaction of the full (100%) mutation score. For finite behavioural models, the Equivalent Mutant Problem (EMP) can be addressed through language equivalence of non-deterministic finite automata, which is a well-studied, yet computationally expensive, problem in automata theory. In this paper, we report on our preliminary assessment of a state-of-the-art exact language equivalence tool to handle the EMP against 3 models of size up to 15,000 states on 1170 mutants. We introduce random and mutation-biased simulation heuristics as baselines for comparison. Results show that the exact approach is often more than ten times faster in the weak mutation scenario. For strong mutation, our biased simulations are faster for models larger than 300 states. They can be up to 1,000 times faster while limiting the error of misclassifying non-equivalent mutants as equivalent to 10% on average. We therefore conclude that the approaches can be combined for improved efficiency.

The use of lists in the study of undecidable problemsin automata theory

There are many decision problems in automata theory (including membership, emptiness, emptiness of intersection, inclusion and universality problems) that for some classes of tree automata are NP-hard. The study of their parameterized complexity allows us to find new bounds of their non-polynomial time algorithmic behaviors. We present results of such a study for classical tree automata (TA), rigid tree automata (RTA), tree automata with global equality and disequality (TAGED) and t-DAG automata.KeywordsModel CheckParameterized ComplexityLinear Temporal LogicFinite AutomatonGlobal ConstraintThese keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.

On Oscillation-free ε-random Sequences

Checking whether one formal language is included in another is vital to many verification tasks. In this paper, we provide solutions for checking the inclusion of the languages given by visibly pushdown automata over both finite and infinite words. Visibly pushdown automata are a richer automaton model than the classical finite-state automata, which allows one, e.g., to reason about the nesting of procedure calls in the executions of recursive imperative programs. The highlight of our solutions is that they do not comprise automata constructions for determinization and complementation. Instead, our solutions are more direct and generalize the so-called Ramsey-based inclusion-checking algorithms, which apply to classical finite-state automata and proved effective there, to visibly pushdown automata. We also experimentally evaluate our algorithms thereby demonstrating the virtues of avoiding determinization and complementation constructions.

Type systems are one backbones of programming language design and implementation. Current research addresses questions in fields as diverse as mathematical logic, program analysis, and human factors engineering. Some of the future challenges for the field are: increasing the expressiveness of typed programming languages, broadening the information carried by types, and making type systems amenable to user definition and customization.

17 Automata-theoretic techniques for temporal reasoning

This volume contains the proceedings of the Tenth International Symposium on Games, Automata, Logic and Formal Verification (GandALF 2019). The symposium took place in Bordeaux, France, from the 2nd to the 3rd of September 2010. The GandALF symposium was established by a group of Italian computer scientists interested in mathematical logic, automata theory, game theory, and their applications to the specification, design, and verification of complex systems. Its aim is to provide a forum where people from different areas, and possibly with different backgrounds, can fruitfully interact. GandALF has a truly international spirit, as witnessed by the composition of the program and steering committee and by the country distribution of the submitted papers.

The present paper proposes a new investigation area in automata theory — jumping finite automata. These automata work like classical finite automata except that they read input words discontinuously — that is, after reading a symbol, they can jump over some symbols within the words and continue their computation from there. The paper establishes several results concerning jumping finite automata in terms of commonly investigated areas of automata theory, such as decidability and closure properties. Most importantly, it achieves several results that demonstrate differences between jumping finite automata and classical finite automata. In its conclusion, the paper formulates several open problems and suggests future investigation areas.

I am a fan of Sheldon Ross' textbooks on probability; they are concise and full of interesting exercises. He and Erol Pek¨oz have just released a second edition of A Second Course in Probability (Cambridge University Press, 2023), which promises a rigorous but accessible and modern introduction to a selection of advanced topics in the field. Javier Esparza's work includes using automata to study model checking, program analysis and verification. His book (coauthored with Michael Blondin) Automata Theory: An Algorithmic Approach (The MIT Press, 2023) emphasizes efficient constructions of (ω-)automata and other algorithmic concerns. Filterworld: How Algorithms Flattened Culture by New Yorker staff writer Kyle Chayka (Doubleday, 2024) investigates the pervasive impact of algorithms on consumption and distribution of culture and explores ways to reclaim our freedom from the digital overlord.

Benchmarks for text analysis: A response to Budge and Pennings

The concept of utility is used as a decision tool for consumers to choose a commodity. Analyzing consumer behavior is complicated due to the qualitative nature of the utility. Hence, this paper investigates a quantitative method to evaluate the utility of consumers. The methodology is based on linguistic expressions of fuzzy logic. Initially, the authors identify different parameters being effective on utility of a consumer. Then, using fuzzy linguistic expressions the quantitative value of utility are determined. Also some statistical analyses are set to investigate the effective parameters on the utility. Consequently, the optimization is done applying mathematical nonlinear programming. Some analysis is performed as sensitivity study. A case study is conducted to verify the applicability and effectiveness of the proposed methodology.