Fragment Of First-order Logic Research Articles

Positive First-order Logic on Words and Graphs

We study FO+, a fragment of first-order logic on finite words, where monadic predicates can only appear positively. We show that there is an FO-definable language that is monotone in monadic predicates but not definable in FO+. This provides a simple proof that Lyndon's preservation theorem fails on finite structures. We lift this example language to finite graphs, thereby providing a new result of independent interest for FO-definable graph classes: negation might be needed even when the class is closed under addition of edges. We finally show that the problem of whether a given regular language of finite words is definable in FO+ is undecidable.

The Modelwise Interpolation Property of Semantic Logics

In this paper we introduce the modelwise interpolation property of a logic that states that whenever \(\models\phi\to\psi\) holds for two formulas \(\phi\) and \(\psi\), then for every model \(\mathfrak{M}\) there is an interpolant formula \(\chi\) formulated in the intersection of the vocabularies of \(\phi\) and \(\psi\), such that \(\mathfrak{M}\models\phi\to\chi\) and \(\mathfrak{M}\models\chi\to\psi\), that is, the interpolant formula in Craig interpolation may vary from model to model. We compare the modelwise interpolation property with the standard Craig interpolation and with the local interpolation property by discussing examples, most notably the finite variable fragments of first order logic, and difference logic. As an application we connect the modelwise interpolation property with the local Beth definability, and we prove that the modelwise interpolation property of an algebraizable logic can be characterized by a weak form of the superamalgamation property of the class of algebras corresponding to the models of the logic.

Non-distributive positive logic as a fragment of first-order logic over semilattices

Abstract We characterize non-distributive positive logic as the fragment of a single-sorted first-order language that is preserved by a new notion of simulation called a meet-simulation. Meet-simulations distinguish themselves from simulations because they relate pairs of states from one model to single states from another. En route to this result, we use a more traditional notion of simulations and prove a Hennessy–Milner-style theorem for it, using an analogue of modal saturation called meet-compactness.

Finite Model Property and Bisimulation for LFD

Recently, Baltag and van Benthem introduced a decidable logic of functional dependence (LFD) that extends the logic of Cylindrical Relativized Set Algebras (CRS) with atomic local dependence statements. Its semantics can be given in terms of generalised assignment models or their modal counterparts, hence the logic is both a first-order and a modal logic. We show that LFD has the finite model property (FMP) using Herwig's theorem on extending partial isomorphisms, and prove a bisimulation invariance theorem characterizing LFD as a fragment of first-order logic.

The fluted fragment with transitive relations

The fluted fragment is a fragment of first-order logic (without equality) in which, roughly speaking, the order of quantification of variables coincides with the order in which those variables appear as arguments of predicates. It is known that this fragment has the finite model property. We consider extensions of the fluted fragment with various numbers of transitive relations, as well as the equality predicate. In the presence of one transitive relation (together with equality), the finite model property is lost; nevertheless, we show that the satisfiability and finite satisfiability problems for this extension remain decidable. We also show that the corresponding problems in the presence of two transitive relations (with equality) or three transitive relations (without equality) are undecidable, even for the two-variable sub-fragment.

Logics of dependence and independence: The local variants

Abstract Modern logics of dependence and independence are based on team semantics, which means that formulae are evaluated not on a single assignment of values to variables, but on a set of such assignments, called a team. This leads to high expressive power, on the level of existential second-order logic. As an alternative, Baltag and van Benthem have proposed a local variant of dependence logic, called logic of functional dependence ($ {\textsf {LFD}}$). While its semantics is also based on a team, the formulae are evaluated locally on just one of its assignments, and the team just serves as the supply of the possible assignments that are taken into account in the evaluation process. This logic thus relies on the modal perspective of generalized assignments semantics and can be seen as a fragment of first-order logic. For the variant of $ {\textsf {LFD}}$ without equality, the satisfiability problem is decidable. We extend the idea of localizing logics of dependence and independence in a systematic way, taking into account local variants of standard atomic dependency properties: besides dependence and independence, also inclusion, exclusion and anonymity. We study model-theoretic and algorithmic questions of the localized logics and also resolve some of the questions that had been left open by Baltag and van Benthem. In particular, we study decidability issues of the local logics and prove that satisfiability of $ {\textsf {LFD}}$ with equality is undecidable. Further, we establish characterization theorems via appropriate notions of bisimulation and study the complexity of model checking problems for these logics.

First-order logic as a constraint satisfaction problem

In this paper, we discourse an analysis of classical first-order predicate logic as a constraint satisfaction problem, CSP. First, we will offer our general framework for CSPs, and then apply it to first-order logic. We claim it would function as a new semantics, constraint semantics, for logic. Then, we prove the soundness and completeness theorems with respect to the constraint semantics. The latter theorem, which will be proven by a proof-search method, implies the cut-elimination theorem. Furthermore, using the constraint semantics, we make a new proof of the Craig interpolation theorem. Also, we will provide feasible algorithms to generate interpolants for some decidable fragments of first-order logic: the propositional logic and the monadic fragments. The algorithms, reflecting a ‘projection’ of an indexed relation, will show how to transform given formulas syntactically to obtain interpolants.

A model-theoretic approach to descriptive general frames: the van Benthem characterization theorem

AbstractThe celebrated van Benthem characterization theorem states that on Kripke structures modal logic is the bisimulation-invariant fragment of first-order logic. In this paper, we prove an analogue of the van Benthem characterization theorem for models based on descriptive general frames. This is an important class of general frames for which every modal logic is complete. These frames can be represented as Stone spaces equipped with a ‘continuous’ binary relation. The proof of our theorem generalizes Rosen’s proof of the van Benthem theorem for finite frames and uses as an essential technique a new notion of descriptive unravelling. We also develop a basic model theory for descriptive general frames and show that in many ways it behaves like the model theory of finite structures. In particular, we prove the failure of the compactness theorem, of the Beth definability theorem, of the Craig interpolation theorem and of the upward Löwenheim–Skolem theorem.1

An optimal cut-off algorithm for parameterised refinement checking

• The cut-off set problem of a parameterised system is expressed in first-order logic. • An SMT-based semi-algorithm for computing a cut-off set is presented. • The algorithm terminates for topologies expressed in the E*A* fragment of FOL. • Upon termination, the algorithm produces the optimal cut-off set. • The algorithm is applied to the leader election phase of (Byzantine) Raft. The verification of contemporary distributed software systems is challenging, because they are heavily parameterised, containing components whose number and connections cannot be a priori fixed. In this work, we consider the multi-parameterised verification of safety properties by refinement checking in the context of labelled transition systems (LTSs). The LTSs are parameterised by using first-order constructs, sorts, variables, and predicates, while preserving compositionality. This allows us to parameterise not only the number of replicated components but also the communication topology of the system. Our approach to solving a verification task in the parameterised LTS formalism is to determine a finite cut-off set of parameter values such that in order to prove a parameterised system implementation correct with respect to its specification, it is sufficient to consider only finitely many instances of the parameterised system generated by the parameter values in the cut-off set. In the conference version of this work, we converted the problem of determining a finite cut-off set into the unsatisfiability of a first-order formula and provided a satisfiability modulo theories (SMT)-based semi-algorithm for dynamically, i.e., iteratively, computing a cut-off set. In this article, we present a new version of the algorithm and prove that the cut-off sets computed by this new algorithm are optimal. Hence, we call the new version the optimal cut-off algorithm. The algorithm will always terminate for system topologies expressible in the ∃ ⁎ ∀ ⁎ fragment of first-order logic. It also enables us to consider systems with topologies beyond this fragment, but for these systems, the algorithm is not guaranteed to terminate. We have implemented the approach on top of the Z3 SMT solver and successfully applied it to several system models. As a running example, we consider the leader election phase of the generalised (Byzantine) Raft consensus algorithm and prove the optimal cut-off set of six (respectively, thirteen) parameter values corresponding to instances up to three (respectively, four) servers. To the best of our knowledge, this is the first time a Byzantine variant of the parameterised Raft leader election is automatically verified.

Losing connection: the modal logic of definable link deletion

Abstract In this article, we start with a two-player game that models communication under adverse circumstances in everyday life and study it from the perspective of a modal logic of graphs, where links can be deleted locally according to definitions available to the adversarial player. We first introduce a new language, semantics and some typical validities. We then formulate a new type of first-order translation for this modal logic and prove its correctness. Then, a novel notion of bisimulation is proposed that leads to a characterization theorem for the logic as a fragment of first-order logic, and a further investigation is made of its expressive power against hybrid modal languages. Next, we discuss how to axiomatize this logic of link deletion, using dynamic-epistemic logics as a contrast. Finally, we show that our new modal logic lacks both the tree model property and the finite model property and that its satisfiability problem is undecidable.

Semantic Approach to Data Integration for an Internet of Things Supporting Apparel Supply Chain Management

Abstract The rapid development of the Internet of Things (IoT) and the huge growth of valuable data produced by decentralising information processing along global apparel supply chain have led to a persuasive appeal for a semantic approach to integrating distributed data facilities in the field of self-determining collaborating logistics services. This paper describes a framework, Apparel Business Decentralised Data Integration (ABDDI), which exploits knowledge representation techniques and languages (e.g. Description Logics – DLs) to annotate relevant business activities, movements of products within the manufacturing network to provide value-added services. More specifically the paper discusses the DLs formalisms, which are used for knowledge representation in a decidable fragment of First Order Logic; and ALN (D) (Attributive Language with unqualified Number restrictions and concrete Domains) related issues. The paper presents an algorithm to demonstrate the DLs based entity concept similarity assessment to facilitate semantic web service. Finally, a business scenario is used to present some of the knowledge representation formalisms and concept similarity assessment in ABDDI.

Subsequence versus substring constraints in sequence pattern languages

A family of logics for expressing patterns in sequences is investigated. The logics are all fragments of first-order logic, but they are variable-free. Instead, they can use substring and subsequence constraints as basic propositions. Propositions expressing constraints on the beginning or the end of the sequence are also available. Also wildcards can be used, which is important when the alphabet is not fixed, as is typical in database applications. The maximal logic with all four features of substring, subsequence, begin–end constraints, and wildcards, turns out to be equivalent to the family of star-free regular languages of dot-depth at most one. We investigate the lattice formed by taking all possible combinations of the above four features, and show it to be strict. For instance, we formally confirm what might intuitively be expected, namely, that boolean combinations of substring constraints are not sufficient to express subsequence constraints, and vice versa. We show an expressiveness hierarchy results from allowing multiple wildcards. We also investigate what happens with regular expressions when concatenation is replaced by subsequencing. Finally, we study the expressiveness of our logic relative to first-order logic.

Ultimate TreeAutomizer (CHC-COMP Tool Description)

We present Ultimate TreeAutomizer, a solver for satisfiability of sets of constrained Horn clauses. Constrained Horn clauses (CHC) are a fragment of first order logic with attractive properties in terms of expressiveness and accessibility to algorithmic solving. Ultimate TreeAutomizer is based on the techniques of trace abstraction, tree automata and tree interpolation. This paper serves as a tool description for TreeAutomizer in CHC-COMP 2019.

Zero­one laws for sentences with k variables

We consider the k variable fragment of first order logic on graphs. We claim that, for α≤1κ-1, the random graph G(n, n-α) obeys zero­one law w.r.t. this logic. Moreover, for every ε > 0 , there exists α∈1κ-1,1κ-1+ε such that G(n, n-α) does not obey the law.

Universal first-order logic is superfluous in the second level of the polynomial-time hierarchy

Abstract In this paper we prove that $\forall \textrm{FO}$, the universal fragment of first-order logic, is superfluous in $\varSigma _2^p$ and $\varPi _2^p$. As an example, we show that this yields a syntactic proof of the $\varSigma _2^p$-completeness of value-cost satisfiability. The superfluity method is interesting since it gives a way to prove completeness of problems involving numerical data such as lengths, weights and costs and it also adds to the programme started by Immerman and Medina about the syntactic approach in the study of completeness.

SOME MODEL THEORY OF GUARDED NEGATION

AbstractThe Guarded Negation Fragment (GNFO) is a fragment of first-order logic that contains all positive existential formulas, can express the first-order translations of basic modal logic and of many description logics, along with many sentences that arise in databases. It has been shown that the syntax of GNFO is restrictive enough so that computational problems such as validity and satisfiability are still decidable. This suggests that, in spite of its expressive power, GNFO formulas are amenable to novel optimizations. In this article we study the model theory of GNFO formulas. Our results include effective preservation theorems for GNFO, effective Craig Interpolation and Beth Definability results, and the ability to express the certain answers of queries with respect to a large class of GNFO sentences within very restricted logics.

Modal logics of sabotage revisited

Sabotage modal logic was proposed in 2003 as a format for analysing games that modify graphs they are played on. We investigate some model-theoretic and proof-theoretic aspects of sabotage modal logic, which has come to be viewed as an early dynamic logic of graph change. Our first result is a characterization theorem for sabotage modal logic as a fragment of first-order logic which is invariant with respect to a natural notion of ‘sabotage bisimulation’. Next, we offer a sound and complete tableau method and its associated labelled sequent calculus for analysing reasoning in sabotage modal logic. Finally, we identify and briefly explore a number of open research problems concerning sabotage modal logic that illuminate its complexity, placing it within the current landscape of modal logics that analyse model update, and, returning to the original motivation of sabotage, fixed-point logics for network games.

On the Complexity of the Model Checking Problem

The complexity of the model checking problem for various fragments of first-order logic (FO) has attracted much attention over the last two decades, in particular for the fragment induced by $\exists$ and $\wedge$ and that induced by $\forall, \exists$, and $\wedge$, which are better known as the constraint satisfaction problem and the quantified constraint satisfaction problem, respectively. The former was conjectured to follow a dichotomy between P and NP-complete by Feder and Vardi [SIAM J. Comput., 28 (1998), pp. 57--104]. For the latter, there are several partial trichotomy results between P, NP-complete, and Pspace-complete, and Chen [Meditations on quantified constraint satisfaction, in Logic and Program Semantics, Springer, Heidelberg, 2012, pp. 35--49] ventured a conjecture regarding Pspace-completeness vs. membership in NP in the presence of constants. We give a comprehensive account of the whole field of the complexity of model checking similar syntactic fragments of FO. The above two fragments...

Algorithms for Deciding Counting Quantifiers over Unary Predicates

We study algorithms for fragments of first order logic ex- tended with counting quantifiers, which are known to be highly complex in general. We propose a fragment over unary predicates that is NP-complete and for which there is a nor- mal form where Counting Quantification sentences have a single Unary predicate, thus call it the CQU fragment. We provide an algebraic formulation of the CQU satisfiability problem in terms of Integer Linear Programming based on which two algorithms are proposed, a direct reduction to SAT instances and an Integer Linear Programming version extended with a column generation mechanism. The latter is shown to lead to a viable implementation and experiments shows this algorithm presents a phase transition behavior.

Expressive Power of Abstract Meaning Representations

The syntax of abstract meaning representations (AMRs) can be defined recursively, and a systematic translation to first-order logic (FOL) can be specified, including a proper treatment of negation. AMRs without recurrent variables are in the decidable two-variable fragment of FOL. The current definition of AMRs has limited expressive power for universal quantification (up to one universal quantifier per sentence). A simple extension of the AMR syntax and translation to FOL provides the means to represent projection and scope phenomena.