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新论文 · v1arXiv:2611.17235

Al-Ghasali:基于有限状态自动机与大语言模型模拟伊斯兰教法裁决的计算框架

Al-Ghasali: A Computational Framework for Simulating Islamic Jurisprudential Rulings via Finite State Automata and Large Language Models

Elnaserledinellah Mahmoud Abdelwahab

AI 速读 基于摘要

该论文提出 Al-Ghasali 框架,将封闭教法章节的语义形式化为确定性有限状态自动机,并用其严格约束大语言模型生成可读的教法摘要。

cs.AI · cs.FL

查看原文摘要

This paper presents Al Ghasali, a computational framework designed to formalize and simulate Islamic jurisprudential (Fiqh) rulings. Building upon recent set theoretic formalizations of al sabr wa al Taqsim that extract minimal operational rules as simple Horn clause logical programs, this work proves that the semantics of closed Fiqh chapters collapse completely to deterministic Finite State Automata (FSA). We establish a formal computational hierarchy, demonstrating that restricting formalization to finite propositional Horn theories guarantees decidability and constant time (O(1)) verdict extraction after offline compilation. The framework formally proves that hierarchical compositions of sub-chapter FSAs preserve this O(1) complexity, and that temporal juristic requirements, such as Tartib (order), are deterministically flattened into static ontological states, preserving the memoryless property of the automaton. To generate human-readable juristic summaries, Al Ghasali incorporates Large Language Models (LLMs) via an architecture where the deterministic FSA strictly controls the probabilistic LLM. Crucially, the paper formulates sufficient design safety conditions for this FSA LLM integration, ensuring strict adherence to the epistemological boundaries of Usul al Fiqh. To neutralize the risk of LLM hallucination, the system employs a Grammar Guided Constrained Decoding mechanism. We formally define the mapping function that dynamically constructs unambiguous right linear grammars from the FSA execution history. The paper mathematically proves that this architecture, augmented by a Bounded Neutral Lexicon and Valence Locking, guarantees the absolute absence of Decisional Hallucination, Juristic Factual Hallucination, and Semantic Inversion reducing the LLM to a pure linguistic transformer of deterministic juristic facts

版本更新 · v3arXiv:2605.13385

Exact Accepting-State Spectrum for Reversal of Permutation Automata

Samuel German

原文摘要

In this paper we determine the accepting-state spectrum of the reversal operation on permutation automata, and moreover prove the conjecture conjectured by Rauch and Holzer in so doing. Namely, we show that reversal satisfies the spectrum $g^{\operatorname{asc}}_{R,\mathrm{PFA}}(0)=\{0\}$, $g^{\operatorname{asc}}_{R,\mathrm{PFA}}(1)=\{1\}$, and $g^{\operatorname{asc}}_{R,\mathrm{PFA}}(m)=\mathbb{N}_{\ge 2}$ for $m\ge 2$. We do this by, for every $m\ge 2$ and every $α\ge 2$, constructing a binary permutation automaton $A_{m,α}$ such that $ \operatorname{asc}(L(A_{m,α}))=m$ and $ \operatorname{asc}(L(A_{m,α})^{R})=α$. The spectrum above follows from this (combined with the trivial cases $m=0$ and $m=1$ and the fact that $1$ is magic for every $m\ge 2$). Thus our result shows that for $m \ge 2$, the reversal operation in permutation automaton attains ever single value positive value in the accepting-state complexity except for $1$.

cs.FL

新论文 · v1arXiv:2611.16562

The Regular Cover Problem is NP-complete

Stefan Hetzl, Parham Shadman

原文摘要

The regular cover problem is the following question: given a finite language $L$ and a $k\geq 0$, is there an acyclic regular grammar $G$ with at most $k$ productions that covers $L$, i.e., that satisfies $L(G) \supseteq L$. The study of this problem is motivated by applications in proof theory and automated deduction. The regular cover problem is known to be in NP. In this paper we show that it is NP-complete by reducing the vertex cover problem for graphs with maximum degree three to it.

cs.FL

版本更新 · v5arXiv:2104.02876

Finite Automata Encoding Piecewise Polynomials

Dmitry Berdinsky, Prohrak Kruengthomya

原文摘要

Finite automata are used to encode geometric figures and functions. The original approach is to represent each point of a figure in $\mathbb{R}^n$ as a convolution of its $n$ coordinates written in some base. Then a figure is said to be encoded as a finite automaton if the set of convolutions corresponding to the points in this figure is accepted by a Büchi automaton. The only differentiable functions which can be encoded as a finite automaton in this way are linear. This paper proposes a discretization of the original approach in which we change points as building blocks of a function to hierarchical tensor product B-splines. This reduces an uncountable set of points representing a function to a countable set of splines that enables us to use finite automata instead of Büchi automata. Moreover, it allows to represent a rich family of piecewise polynomial functions with arbitrary degrees of smoothness that can approximate any continuous functions defined on a compact domain arbitrarily close. We consider such piecewise polynomial functions with unbounded support and demonstrate that finite automata allow to handle computational tasks arising in the framework of hierarchical splines in polynomial time.

cs.CG · cs.FL

新论文 · v1arXiv:2611.14887

Characterizing Local Breadth in Language Generation

Jon Kleinberg, Fan Wei

原文摘要

Large language models sharpen the validity--breadth trade-off: a generator should avoid hallucinations without collapsing onto a narrow set of valid outputs. We study generation from positive examples of an unknown target in the Kleinberg--Mullainathan model, with arbitrary, possibly adversarial order and no distributional or computational assumptions. Breadth is measured by lower Banach density, which rules out arbitrarily large sparse holes, unlike prefix-based lower asymptotic density. 1. Exact optima in one dimension: For each target $K$ in a countable family, we characterize its optimal lower Banach density $b(K)$ via equivalent combinatorial and topological formulations. One eventually valid generator attains all $b(K)$ simultaneously. Every $α\in[0,1/2]$ occurs as $b(K)$ in some countable family; finite Cantor--Bendixson point rank guarantees $b(K)=1/2$, even without a uniform rank bound. 2. Unavoidable trade-offs in higher dimensions: For $d\ge2$, there need not be a single best generator: optimizing density for one target may worsen the guarantee for another. An explicit family quantifies this intrinsically multi-objective trade-off. 3. Complete characterization of density profiles: We characterize the full region of simultaneously achievable guarantees, with equivalent combinatorial and topological formulations, after excluding geometrically degenerate rectangles. Every prescribed product $\prod_i[0,α_i]$, $α_i\in[0,1/2]$ can occur as an exact achievable region for some language collection. 4. Near-half guarantees and the sharp endpoint: Under a near-logarithmic nondegeneracy condition, one generator achieves filtered density at least $1/2-\varepsilon$ at all finite-point-rank targets, for every $\varepsilon>0$, improving the previous polylogarithmic threshold. The exact $1/2$ endpoint can fail even for a rank-zero singleton family.

cs.DS · cs.FL · cs.LG · stat.ML

版本更新 · v2arXiv:2610.39941

插入的块交换下降:交换投影与最小掩码

Block-exchange descent for insertion: commuting projections and minimum masks

Haobo Ma, Wenlin Zhang, Charles E. Hughes

AI 速读 基于摘要

研究shuffle表示中最小插入度在块交换下的下降规律,并给出交换投影下的精确刻画与若干计算机辅助验证结果。

cs.FL · math.CO

查看原文摘要

For fixed nonempty words $u,v$, the minimum insertion degree of a shuffle is the least number of inserted-source runs among its representations. We prove that, after a block exchange from a minimum mask of degree $r$, the minimum over masks with commuting source projections is exactly $r-1$; a larger decrease occurs precisely when a noncommuting mask has fewer runs. If either source is unary, every such exchange is exact. We prove an explicit repair for an infinite periodic degree-three family. Computer-assisted results establish first-mask descent through combined length seventeen over every alphabet, degree-three first-mask descent through length thirty, and a uniform repair of all degree-three failures through length thirty, including all further letter identifications. Counterexamples to arbitrary, first, and last minimum-mask choices explain the need for alternative masks. Finally, we prove that minimum iteration depths have no gaps for arbitrary languages. General block-exchange descent and Singleton No-Gap remain open.

版本更新 · v2arXiv:2605.10852

置换自动机右商接受状态谱的一元到非一元转变

A Unary-to-Nonunary Transition in the Accepting-State Spectrum of Right Quotient for Permutation Automata

Samuel German

AI 速读 基于摘要

作者报告置换自动机右商运算的接受状态谱在任意字母表下由一元情形的有限区间变为全部正整数,从而解决了 Rauch 与 Holzer 提出的开放问题。

cs.FL

查看原文摘要

This paper determines the accepting-state spectrum of the right-quotient operation for permutation automata, solving an open problem posed by Rauch and Holzer. They showed that in the unary case in which the languages whose right quotient we consider are languages over an alphabet with but one symbol, the accepting state complexities which could ensue for automata recognizing their quotient is exactly all integers between $1$ and $mn$ inclusive when $m,n \ge 1$; we show that for arbitrary alphabets the accepting-state spectrum is $g^{\operatorname{asc}}_{-1,\mathrm{PFA}}(m,n)=\{0\}$ if $m=0$ or $n=0$, and $g^{\operatorname{asc}}_{-1,\mathrm{PFA}}(m,n)=\mathbb{N}_{>0}$ if $m,n\ge 1$. Our result shows that every positive accepting-state complexity ensues for right quotient as long as both of the languages of which we consider the right quotient are nonempty. $0$ becomes the only unavoidable magic value. Moreover, we show that an alphabet with just two letters can witness any arbitrary $α\ge 1$ when $m,n \ge 1$, in that languages can be defined over a binary alphabet with accepting-state complexity $m$ and $n$ respectively for which their right quotient has accepting-state complexity $α$. What ultimately happens in our proof is that we construct $(A^{\mathrm q}_{m,α},B^{\mathrm q}_{n,α})$ such that the words accepted by $B^{\mathrm q}_{n,α}$ induce a point stabilizer in a symmetric group, and the standard quotient construction giving an automaton recognizing the quotient language then saturates the original final set of $A^{\mathrm q}_{m,α}$ to a full orbit; this gives a minimal quotient automaton with exactly $α$ final states. The complete spectrum which is our result follows from this, solving the open question of what the right quotient's accepting-state complexity for permutation automata is.

版本更新 · v2arXiv:2610.07044

An exact compress-with-another threshold in a binary automaton family

Qichao Wang, Daoyu Dong

原文摘要

For a state $q$ in a synchronizing automaton, let $μ(q)$ be the minimum length of a word merging $q$ with another initial state. Szykuła asked whether $μ(q)=O(n)$ for strongly connected synchronizing automata and described a binary family attributed to Dżyga, with $n=3p$ states and a conjectured threshold $4n/3$. We specify the boundary transitions omitted from the published piecewise definition and prove that the resulting automata $\mathcal A_p$ satisfy $μ(q_0)=4p=4n/3$ for all $p\geq3$. A shortest word merging $q_0$ with another state is $(ba)^p(ab)^p$. We also construct a reset word of length $3p^2+4p-1$. Consequently, any uniform linear upper bound for $μ(q)$ on binary strongly connected synchronizing automata with corank-one letters has leading constant at least $4/3$.

cs.FL · math.CO

版本更新 · v6arXiv:2511.15238

A Quantitative Approach to Reach-Avoid Reachability Analysis for Discrete-Time Nonlinear Control Systems

Ihab Tabbara, Eliya Badr, Hussein Sibai

原文摘要

A reach-avoid specification requires a dynamical system to reach a target set of states while avoiding a failure set. Reachability analysis partitions the state space into parts starting from which the specification can be satisfied by following some control signal and those from which it cannot despite the best control effort. In this paper, we present a quantitative approach for reachability analysis to analyze the satisfaction of avoid and reach-avoid specifications for discrete-time nonlinear control systems. In such an approach, a value function assigns a value to each state that determines how robustly the system satisfies or violates the specification starting from it and following the optimal control signal. However, computing such a value function is difficult. Instead, our approach constructs discrete abstractions on which it performs value iteration to compute sound bounds on the desired value function. The resulting lower bound enables a sound under-approximation of the reach-avoid set (RAS) and, in the avoid case, a sound over-approximation of the backward reachable set (BRS). When the control set is finite, the upper bound additionally enables a sound over-approximation of the RAS and, in the avoid case, a sound under-approximation of the BRS. Moreover, the obtained bounds provide quantitative guarantees on safety margins and, in discounted reach-avoid problems, on safe target-reaching times. When the control set is finite, they also bound failure-reaching times. Our approach further refines the abstraction by splitting the grid cells that could not be classified as within or outside the BRS (or RAS) to improve the bounds. We evaluate our approach on five systems with up to five-dimensional state spaces.

eess.SY · cs.FL · cs.SC

新论文 · v1arXiv:2611.13061

The Left Ripple of Byte-Pair Encoding: Certified Lookbehind for Every Dictionary

Nicklas Nidhögg

原文摘要

Berglund and van der Merwe formalized byte-pair encoding and bounded how far an appended string can change a tokenization, leaving the converse open: how far can a string prepended on the left change it, which dictionaries make that ripple infinite, and can it be computed efficiently when finite? We answer all three for every dictionary. The origin radius, how far a prepend can change covering spans, is decided with radius certificates by a product of two runs of the automaton that guesses the final tokens, in time polynomial in the dictionary written out, and it is infinite exactly when one periodic word has two canonical tilings with no common boundary. Under their ordering condition it is infinite exactly when some rule (t, t) finds its two copies adjacent at its own stage, and such a rule makes any dictionary infinite. A finite radius makes every window of a width read off the radii have a cut, and the radius is finite exactly when such cuts are dense. The token machine completes for every dictionary, and the tokenization is subsequential, extending what Berglund, Martens and van der Merwe proved for proper ones under one pass per rule. A streaming tokenizer emits after every symbol exactly the tokens that no continuation changes, in polynomial time, answering a question of Dalirrooyfard and Ye. Boundedness of the label measure, the edit distance of the token sequences, is decided for every dictionary in polynomial time as well, and under the ordering condition the largest distance one edit causes over dictionaries of m rules lies asymptotically between m^2/10 and m^2/2. GPT-2's merge table carries 244 effective self-pairs, so its origin radius is infinite from the forty-second merge on, and that of cl100k, o200k and Llama 3 from their first. Every measured number is its program's output, and what is not executed is named.

cs.FL · cs.CL · cs.DS · cs.PL

新论文 · v1arXiv:2611.12618

Type-logical grammars and formal languages

Richard Moot

原文摘要

We show that type-logical grammars with the standard rules for product, associativity, extraction and infixation have an NP-complete fixed recognition problem, adapting a construction for first-order linear logic from Pshenitsyn (2025), who already showed that grammars in first-order linear logic are closed under intersection and therefore not semilinear and not mildly context-sensitive. We strengthen these results and shown that grammars in first-order linear logic can simulate the quasi-linear grammars of Book \& Greibach (1970), the grammars recognised in non-deterministic linear time (NSPACE(n) or. NLIN). I argue that NLIN is an interesting class of formal languages as well, and a useful upper bound on the time complexity of formalisms used for natural language, just like LOGCFL is a useful upper bound on the space complexity. Taken together this means that first-order linear logic can be seen as the logic of non-deterministic linear-time string languages, graph languages and automata.

cs.CC · cs.CL · cs.FL · cs.LO

新论文 · v1arXiv:2611.12315

Beating Rytter's Bound: All-Pairs CFL Reachability in $O(n^3(\log\log n)^2/(\log n)^2)$ Time

Rupak Majumdar

原文摘要

Context-free reachability and 2NPDA recognition are fundamental problems in program analysis and language theory. Despite years of effort, the best algorithms for these problems run in time $O(n^3/\log n)$ on a word RAM model; they are based on an observation of Rytter in 1985 for 2NPDA which was adapted for CFL reachability by Chaudhuri in 2008. No better algorithm has been designed since. We give the first improvement to Rytter's algorithm. For both all-pairs context-free reachability and 2NPDA recognition, we show a deterministic algorithm running in $O(n^3(\log\log n)^2/(\log n)^2)$ time and $O(n^{2+ε})$ words of space for every fixed $0<ε<1$ on a word RAM. Our improvement is based on a new data structure that reports set differences using batched maintenance of exact intersection counts, allowing saturation to skip regions that contain no new reachability information.

cs.PL · cs.FL

版本更新 · v2arXiv:2312.16336

Learning temporal formulas from examples is hard

Corto Mascle, Nathanaël Fijalkow, Guillaume Lagarde

原文摘要

We study the problem of learning linear temporal logic (LTL) formulas from examples, as a first step towards expressing a property separating positive and negative instances in a way that is comprehensible for humans. Given positive and negative words, the goal is to find a smallest formula satisfied by the positive words and not by the negative ones. We study the computational complexity of this problem for all fragments of negation-free LTL built from the operators F (eventually), G (globally), X (next), $\wedge$ (conjunction), and $\vee$ (disjunction), without the until operator. We show that the problem is in NP for all fragments, that it is in polynomial time for the fragments containing none of the pairs $\{X,\wedge\}$, $\{X,\vee\}$, $\{F,\wedge\}$ and $\{G,\vee\}$, and that it is NP-complete for all other fragments, already for alphabets with two or three letters. We also show that the fragment with only X and $\wedge$ has a polynomial time 3-approximation algorithm, but no polynomial time approximation scheme unless P = NP. These results motivate the search for efficient heuristics.

cs.LG · cs.AI · cs.FL · cs.LO

新论文 · v1arXiv:2611.11572

Closing the Complexity Gap for Wheeler Graph Recognition on $d$-NFAs

Kengo Hashimoto

原文摘要

Wheeler graph recognition asks whether a directed graph whose arcs are labeled by symbols from a totally ordered alphabet admits a Wheeler order, a total order on its vertices compatible with the labels of arcs and the order of their tails. A $d$-NFA is a nondeterministic finite automaton in which at most $d$ transitions with any given label leave each state. For Wheeler graph recognition on $d$-NFAs, Alanko et al. gave a polynomial-time algorithm for $d \leq 2$, whereas Gibney and Thankachan proved NP-completeness for every fixed $d \geq 5$. The computational complexity for $d = 3$ and $d = 4$ remained open. We resolve both open cases by extending the reduction of Gibney and Thankachan with a new encoding of clauses of Not-All-Equal 3-SAT. Specifically, we prove that recognition is NP-complete even for directed acyclic graphs over an ordered binary alphabet with a unique source reaching every vertex and total out-degree at most three at every vertex. Consequently, Wheeler graph recognition on $d$-NFAs is NP-complete for every fixed $d \geq 3$.

cs.CC · cs.FL

版本更新 · v3arXiv:2610.11991

Quantitative Verification of Infinite-State Networks

Dhruv Nevatia, David Basin

原文摘要

Many network protocols and distributed systems combine recursion, unbounded local state, and quantitative behaviour such as cost, latency, or reliability. Existing decidability results for networks of pushdown systems are largely qualitative, and do not extend to quantitative analyses, which must jointly track traces and weights. We present a framework for the quantitative verification of acyclic networks of weighted pushdown systems. Finitely summarising a recursive network component requires collapsing the infinite family of runs obtained by pumping its nested loops, and doing so exactly, rather than by over-approximation, is a standing difficulty. We give a class of weight domains where this is possible: pumping semirings, those in which the weights accumulated by such a family collapse to a closed form; informally, the domain must be unable to count iterations. The class admits domains with infinite ascending chains, such as the arctic semiring and downward-closed languages. Over these, we give a terminating saturation algorithm computing quantitative reachability exactly, resting on two ideas: segment tree algebras, a compositional representation of runs, and thermal extensions, which symbolically separate accelerated weights so that further acceleration remains exact. We use this to compute upward and downward closures of context-free languages uniformly, and to lift the algorithm to acyclic networks over "thin" pumping semirings, yielding the first quantitative safety and reachability analyses for networks of pushdown systems.

cs.FL · cs.LO · cs.PL

新论文 · v1arXiv:2611.11080

Two barriers for minimal time firing squads, with applications to four and five states

Kia Keng Giam

原文摘要

A minimal-time solution of the firing squad synchronization problem synchronizes every line of n cells at time 2n minus 2. Six states suffice; whether five do has been open since 1987. Every line agrees with the half line until its right ends echo returns. For minimal time solutions with any number of states, we prove that cells at distance j behind the half lines front become time-periodic only after time (1.5 minus epsilon)j, for every epsilon greater than 0 and infinitely many j, and that the half line is never periodic in time and space on a wedge at its left border, hence not eventually regular in our sense. With certified satisfiability checks, we exclude four states using the lines of lengths 2 to 5 and parts of the next five, and show that every five state minimal time solution uses at least 15 non quiescent neighbourhoods on its half lines first 78 anti-diagonals. We give five state rules synchronizing exactly the lengths 2 to 14.

cs.FL · nlin.CG

新论文 · v1arXiv:2611.10911

Towards A Parametrized Complexity of Determinization

Ivan Baburin, Ryan Cotterell

原文摘要

Given a nondeterministic finite automaton (NFA), we want to estimate the difficulty of finding an equivalent deterministic finite automaton (DFA). We demonstrate that computing the state complexity of an NFA within polynomial precision is \textsf{PSPACE}-hard, and furthermore the same holds for the complexity of the subset construction, Brzozowski's algorithm, or, indeed, \emph{any} determinization algorithm which runs at least as fast. This result implies that making any \textit{a priori} estimate of the running time of the major determinization algorithms is inherently hard. To circumvent this---in the spirit of parametrized complexity---we try to identify complexity measures which can guarantee efficient determinization. Our main idea rests on linking the complexity of the subset construction to transition monoids using the semigroup complexity. We show that the semigroup complexity by itself can be reasonably approximated for certain classes of NFAs, and then introduce \emph{subset complexity}---a refinement of the semigroup complexity which has a tighter connection with the subset construction. In certain scenarios, the subset complexity can be approximated in polynomial time, making it potentially viable for more practical applications.

cs.FL

版本更新 · v2arXiv:2505.10700

Inquisitive Team Semantics of LTL

Laura Bozzelli, Tadeusz Litak, Munyque Mittelmann, Aniello Murano

原文摘要

In recent years, hyperproperties (i.e., properties of sets of traces) have been identified as a crucial concept for capturing information-flow security policies and knowledge of agents in distributed systems. In the synchronous linear-time setting, a well-known approach for the specification of hyperproperties is based on the set semantics of standard LTL. The resulting logic (TeamLTL) inherits the powerful split interpretation of disjunction from dependence logic. In this paper, we introduce a novel team semantics of LTL inspired by inquisitive logic, whose main features are the intuitionistic interpretation of implication and the inquisitive semantics of disjunction. We investigate expressiveness, decidability, and complexity issues of the novel logic that we call InqLTL and its extension with strong negation. We show that InqLTL with strong negation is highly undecidable and strictly less expressive than TeamLTL with strong negation. On the positive side, we identify a meaningful fragment of InqLTL with a decidable model-checking problem that can express relevant classes of hyperproperties. To the best of our knowledge, this fragment represents the first hyper logic with a decidable model-checking problem that allows unrestricted use of temporal modalities and conditional second-order universal quantification over system refinements via intuitionistic implication.

cs.LO · cs.FL

新论文 · v1arXiv:2611.10136

Automata for MSO over Infinite Trees with Quantification over Borel Sets of Branches

Mikołaj Bojańczyk, Antonio Casares, Sven Manthe, Paweł Parys

原文摘要

Rabin's Tree Theorem says that the MSO theory of the infinite binary tree $2^*$ is decidable. Shelah showed that MSO logic becomes undecidable if this tree is extended to $2^{\le ω}$, i.e. by allowing quantification over sets of infinite branches. A longstanding open problem is whether the decidability can be recovered in $2^{\le ω}$ by restricting set quantification to Borel sets. We make some progress in this direction, by identifying a suitable automaton model, and showing that most of the automata-theoretic approach to Rabin's Theorem can be extended to the new framework. The only missing part is a conjecture about finite-memory determinacy in certain games. This paper states and explores the conjecture. We prove it in some restricted cases, and give lower bounds on the memory required in those games.

cs.FL · cs.LO

版本更新 · v3arXiv:2602.07473

Approximating the Reachability Value of Posterior-Deterministic POMDPs

Nathanaël Fijalkow, Arka Ghosh, Roman Kniazev, Guillermo A. Pérez, Pierre Vandenhove

原文摘要

We introduce posterior-deterministic POMDPs, and we show that for this class of POMDPs, the maximal probability of reaching a given set of states can be approximated up to arbitrary precision. A POMDP is posterior-deterministic if the next state can be uniquely determined by the current state, the action taken, and the observation received. In particular, once the current state is known, it remains known forever. The class contains, for instance, multiple-environment MDPs equipped with a prior distribution over the environments, quasi-deterministic POMDPs, and the episodic version of the classical Tiger POMDP (Kaelbling et al. 1998).

cs.AI · cs.FL

版本更新 · v2arXiv:2602.12300

Fast and General Automatic Differentiation for Finite-State Methods

Lucas Ondel Yang, Caio Corro, Nicolas Denier, Martin Kocour, Tina Raissi, Pablo Riera

原文摘要

We propose a new method, that we coined the ``morphism-trick'', to integrate custom implementations of vector-Jacobian products in automatic differentiation softwares, applicable to a wide range of semiring-based computations. Our approach leads to efficient and semiring-agnostic implementations of the backward pass of dynamic programming algorithms. For the particular case of finite-state methods, we introduce an algorithm that computes and differentiates the $\oplus$-sum of all paths' weight of a finite-state automaton. Results show that, with minimal effort from the user, our novel library allows computing the gradient of a function w.r.t. to the weights of a finite state automaton orders of magnitude faster than state-of-the-art automatic differentiation systems. Implementations are made available via an open-source library distributed under a permissive license.

cs.FL · cs.AI

新论文 · v1arXiv:2611.09157

Word Subtraction Games

Yusuke Inoue, Hiroki Inazu

原文摘要

This note is a self-contained text on word subtraction games, combinatorial games in which players alternately remove a nonempty suffix belonging to a prescribed subtraction set from the current word. It collects and develops basic results on these games from the viewpoints of combinatorial game theory and formal language theory. We focus on the relationship between subtraction sets and the resulting languages of winning and losing positions. The topics include finite, regular, and context-free subtraction sets, as well as several variants and further developments.

cs.FL

新论文 · v1arXiv:2611.09136

Shortest Synchronizing Words on Product Automata

Henning Fernau, Igor Rystsov

原文摘要

We consider some operations on finite automata graphs, in particular various product, union and merge operations, and investigate how they relate to the parameter~$\mathrm{rt}$, the \emph{length of a shortest synchronizing word}. We derive some lower and upper bounds for the operations that we study. We also examine several classes of automata (for instance, partially ordered, commutative or idempotent automata) that are preserved under these operations and show in which way the parameter $\mathrm{rt}$ behaves in these automata classes. Also, we consider automata classes that can be constructed by combining automata from better known classes; in particular, these new classes of automata will also satisfy the bound of the famous Černý conjecture. This also motivates us to study even more closure properties. In particular, we show that certain automata classes related to synchronization form pseudo-varieties. We also commence a similar study concerning the length of shortest homing sequences of Mealy automata.

cs.FL

版本更新 · v3arXiv:2602.24279

A quadratic lower bound for 2DFAs against one-way liveness

Kehinde Adeogun, Christos Kapoutsis

原文摘要

We show that every two-way deterministic finite automaton (2DFA) that solves one-way liveness on height h has Omega(h^2) states. This implies a quadratic lower bound for converting one-way nondeterministic finite automata to 2DFAs, which asymptotically matches Chrobak's well-known lower bound for this conversion on unary languages. In contrast to Chrobak's simple proof, which relies on a 2DFA's inability to differentiate between any two sufficiently distant locations in a unary input, our argument can be applied to inputs over any alphabet and is structured around a main lemma that is general enough to potentially be reused elsewhere.

cs.FL

版本更新 · v6arXiv:2603.10733

二元字母表上光滑词的复杂度

The complexity of smooth words over binary alphabets

Julien Cassaigne, Raphaël Henry

AI 速读 基于摘要

该论文研究二元字母表上光滑词与光滑序列的关系,并在复杂度猜想上取得进展:证明任意字母表的下界、偶数字母表的上界,并改进奇数与混合字母表的上界。

cs.FL · math.CO · math.DS

查看原文摘要

Smooth sequences over an alphabet of positive integers $\{a,b\}$ are sequences that are infinitely derivable, the emblematic example being the Oldenburger-Kolakoski sequence $κ$ over $\{1,2\}$. The main way to study their language is to consider a finite version of smooth sequences called smooth words. In this paper we prove that the smooth words are exactly the factors of smooth sequences and we make progress towards the conjecture that the complexity of smooth words over $\{a,b\}$ grows like $Θ\left(n^{\log(a+b)/\log((a+b)/2)}\right)$: we prove the lower bound over any alphabet and the upper bound over even alphabets, and we improve the known upper bound over odd and mixed alphabets. We also provide a dichotomy that links the language, the morphicity and the factor complexity of $κ$.

新论文 · v1arXiv:2611.07781

Reliability-Aware Z-Grammars and Z-Automata over a Credible-Grade Semiring

Sherzod Turaev, Nor Haniza Sarmin, Wan Heng Fong

原文摘要

Fuzzy grammars and weighted automata usually attach to each word a single grade, which records how strongly the word is generated but not how far that record can be trusted. We study weighted grammars and finite automata whose weights are scalar grade-reliability pairs inspired by Z-numbers. Sequential composition multiplies both components, while aggregation selects a derivation by its credible grade, the product of grade and reliability, with ties resolved by grade. On the canonical carrier, in which the weights of zero grade or zero reliability are identified with zero, the resulting structure is a commutative selective semiring, isomorphic to a subsemiring of a lexicographically ordered product, and its credible-grade projection is a homomorphism onto the Viterbi semiring. We compare several alternative combination rules and identify the carriers on which the relevant algebraic laws hold. Standard results on weighted automata then yield a rational characterization and closure properties. We prove that positive credible-grade cuts and selected-run reliability filters of finite automata are regular and effectively constructible for rational weights and thresholds, and we exhibit distinctions that the scalar projection cannot see: a reliability filter that no scalar reweighting of the same one-state automaton implements, nonmonotonicity under the addition of runs, and an unambiguous automaton with no deterministic equivalent although its scalar projection is deterministic. A count-based example illustrates an attestation penalty for grammar rules. The construction concerns scalar pairs, and its extension to arbitrary fuzzy-valued Z-numbers remains open.

cs.FL · cs.LO

版本更新 · v5arXiv:2410.23187

Explorable Parity Automata

Emile Hazard, Olivier Idir, Denis Kuperberg

原文摘要

We define the class of explorable automata on finite or infinite words. This is a generalization of History-Deterministic (HD) automata, where this time non-deterministic choices can be resolved by building finitely many simultaneous runs instead of just one. We show that recognizing HD parity automata of fixed index among explorable ones is in PTime, thereby giving a strong link between the two notions. We then show that recognizing explorable automata is ExpTime-complete, in the case of finite words or parity automata up to index [0, 2]. Additionally, we define the notion of ω-explorable automata on infinite words, where countably many runs can be used to resolve the non-deterministic choices. We show ExpTime-completeness for ω-explorability of automata on infinite words for the safety and coBüchi acceptance conditions. We finally characterize the expressivity of (ω-)explorable automata with respect to the parity index hierarchy.

cs.FL

新论文 · v1arXiv:2611.06303

An Engineering Reading of the Bounded Halting Problem and Observable Properties of a Universal Machine

Sergey Salishev

原文摘要

The halting problem asks whether a program eventually halts, with unrestricted resources. Engineering systems instead certify bounded halting: given a program, an input, and a step budget T, decide whether the program halts within T steps. This paper studies two of its uses. First, it defines an exact finite-budget problem, placing the simulated program and the checker on the same unit-cost timescale, so the checker can be embedded in an adversarial program. A diagonal argument with explicit additive overhead shows that no fixed deterministic checker decides every instance within any fixed fraction of T below one, for large T. In the nondeterministic case, T bounds the branch depth allowed for a stable observable decision. Second, bounded-halting instances give adversarial tests for finitary universality, since a universal model must support arbitrary finite computations as T grows. The tests check resource growth with T, the absence of a fixed deliberation bound, and later access to intermediate data. They separate a fixed model with extendable external resources, a model family that grows with T, and a larger system built around a fixed component. For machine-learning systems, this identifies the resource growth a universality claim assumes and whether it fails for deployed models.

cs.CC · cs.AI · cs.FL · math.LO

版本更新 · v2arXiv:2611.01825

The Scope Grammar of Natural-Language Rules: Counting and Enumerating Readings modulo Logical Equivalence

Sherzod Turaev

原文摘要

A rule written for people fixes its atomic conditions and connectives but leaves open how the connectives are bracketed, and each bracketing is a different logical reading that an autoformalizer must resolve or expose. We study the scope grammar, a deliberately ambiguous context-free grammar whose derivation trees are the readings of a connective skeleton and whose quotient by logical equivalence is what matters downstream. A skeleton with $k$ binary connectives has $C_k$ derivation trees, the $k$-th Catalan number, but far fewer logically distinct readings. For the positive, repetition-free fragment we make the gap exact: through the uniqueness of the read-once normal form we characterize the realizable normal forms by lowest common ancestors and count them with a two-label recurrence over the operator word, verified against exhaustive enumeration up to eleven atoms. The count is invariant under reversal and $\wedge/\vee$ duality; a skeleton is ambiguous if and only if it uses both $\wedge$ and $\vee$, a one-pass test; and the number of classes is at least $2^{\lfloor n/3\rfloor}$. Up to fifteen atoms the alternating pattern is the worst case; its count has a cubic generating function, is the 3-Schröder sequence (OEIS A137842), and grows with base $\varphi^{5/2}\approx3.330$, below the Catalan base 4. We reduce maximality to an inequality on increments, verified to sixteen atoms, and explain why local exchange arguments cannot prove it. We also treat negation, exceptions, and background axioms, where normal-form uniqueness still decides equivalence but counting is open.

cs.FL · cs.CL · cs.LO

新论文 · v1arXiv:2611.05675

Quadratic reset bounds for finite maximal prefix codes

Samrath Singh Chadha

原文摘要

Let $C$ be a finite maximal prefix code of maximum codeword length $k\ge2$. We prove that, whenever the literal decoder of $C$ is synchronizing, it has a reset word of length at most $(k-1)(4k-5)$. The bound is independent of the alphabet and the number of decoder states. Its main ingredient is a short-detection theorem: a linear observation of the decoder, with terminal weight constant on states of depth $k-1$, is either identically zero or nonzero on a word of length at most $2k-3$. The proof uses a first-return decomposition in noncommuting variables and cancellation of a highest-degree coefficient. For codes whose codeword lengths are $k-1$ and $k$, we prove the sharper bound $2(k-1)^2-1$ and characterize equality. The binary code with the single short word $a^{k-1}$ attains this bound for every $k\ge2$; an age representation and a potential on circular arcs give the matching lower bound. Both upper bounds yield polynomial-time constructions in the explicit code size. The mathematical results and the algorithms are formalized in Lean, with polynomial work bounds in a specified binary cost model.

cs.FL