Quantifier Elimination Research Articles

Model theory of adeles I

We study the model theory of the ring of adeles AK of a number field K. We work in the language of rings and various extensions, and obtain quantifier elimination. We give a description of the definable subsets of AKn, for any n≥1, and prove that they are measurable. We introduce some techniques for computing their measures. We describe the definable sets of minimal idempotents in AK. We show that the quotient of the space of adele classes by the action of the maximal compact subgroup of the idele class group is interpretable in the adeles. We give a short proof of decidability of AQ, and consider uniformity of adelic quantifier elimination in the number field.

Expansions of the group of integers by Beatty sequences

We study the model theoretic structure (Z,+,Pr) where r>1 is an irrational number and the elements of Pr are of the form ⌊nr⌋ for some n∈Z∖{0}. We axiomatize this structure and prove a quantifier elimination result. As a consequence, we get that definable subsets are not sparse unless they are finite. We also prove that there are no reducts of this structure expanding (Z,+).

MODEL THEORY OF DERIVATIONS OF THE FROBENIUS MAP REVISITED

AbstractWe prove some results about the model theory of fields with a derivation of the Frobenius map, especially that the model companion of this theory is axiomatizable by axioms used by Wood in the case of the theory $\operatorname {DCF}_p$ and that it eliminates quantifiers after adding the inverse of the Frobenius map to the language. This strengthens the results from [4]. As a by-product, we get a new geometric axiomatization of this model companion. Along the way we also prove a quantifier elimination result, which holds in a much more general context and we suggest a way of giving “one-dimensional” axiomatizations for model companions of some theories of fields with operators.

Reasoning Method between Polynomial Error Assertions

Error coefficients are ubiquitous in systems. In particular, errors in reasoning verification must be considered regarding safety-critical systems. We present a reasoning method that can be applied to systems described by the polynomial error assertion (PEA). The implication relationship between PEAs can be converted to an inclusion relationship between zero sets of PEAs; the PEAs are then transformed into first-order polynomial logic. Combined with the quantifier elimination method, based on cylindrical algebraic decomposition, the judgment of the inclusion relationship between zero sets of PEAs is transformed into judgment error parameters and specific error coefficient constraints, which can be obtained by the quantifier elimination method. The proposed reasoning method is validated by proving the related theorems. An example of intercepting target objects is provided, and the correctness of our method is tested through large-scale random cases. Compared with reasoning methods without error semantics, our reasoning method has the advantage of being able to deal with error parameters.

A Proof of Bel’tyukov–Lipshitz Theorem by Quasi-Quantifier Elimination. I. Definitions and GCD-Lemma

This paper is the first part of a new proof of decidability of the existential theory of the structure 〈 $$\mathbb{Z}$$ ; 0, 1, +, –, ≤, |〉, where | corresponds to the binary divisibility relation. The decidability was proved independently in 1976 by A.P. Bel’tyukov and L. Lipshitz. In 1977, V.I. Mart’yanov proved an equivalent result by considering the ternary GCD predicate instead of divisibility (the predicates are interchangeable with respect to existential definability). Generalizing in some sense the notion of quantifier elimination (QE) algorithm, we construct a quasi-QE algorithm to prove decidability of the positive existential theory of the structure 〈 $${{\mathbb{Z}}_{{ > 0}}}$$ ; 1, $${{\{ a{\kern 1pt} \cdot \} }_{{a \in {{\mathbb{Z}}_{{ > 0}}}}}}$$ , GCD〉. We reduce to the decision problem for this theory the decision problem for the existential theory of the structure 〈 $$\mathbb{Z}$$ ; 0, 1, +, –, ≤, GCD〉. A quasi-QE algorithm, which performs this reduction, will be constructed in the second part of the proof. Transformations of formulas are based on a generalization of the Chinese remainder theorem to systems of the form GCD(ai, bi + x) = di for every $$i \in [1..m]$$ , where ai, bi, di are some integers such that $${{a}_{i}} \ne 0$$ , $${{d}_{i}} > 0$$ .

Model Completeness, Uniform Interpolants and Superposition Calculus

Uniform interpolants have been largely studied in non-classical propositional logics since the nineties; a successive research line within the automated reasoning community investigated uniform quantifier-free interpolants (sometimes referred to as “covers”) in first-order theories. This further research line is motivated by the fact that uniform interpolants offer an effective solution to tackle quantifier elimination and symbol elimination problems, which are central in model checking infinite state systems. This was first pointed out in ESOP 2008 by Gulwani and Musuvathi, and then by the authors of the present contribution in the context of recent applications to the verification of data-aware processes. In this paper, we show how covers are strictly related to model completions, a well-known topic in model theory. We also investigate the computation of covers within the Superposition Calculus, by adopting a constrained version of the calculus and by defining appropriate settings and reduction strategies. In addition, we show that computing covers is computationally tractable for the fragment of the language used when tackling the verification of data-aware processes. This observation is confirmed by analyzing the preliminary results obtained using the mcmt tool to verify relevant examples of data-aware processes. These examples can be found in the last version of the tool distribution.

Expansions and Neostability in Model Theory

AbstractThis thesis is concerned with the expansions of algebraic structures and their fit in Shelah’s classification landscape.The first part deals with the expansion of a theory by a random predicate for a substructure model of a reduct of the theory. Let T be a theory in a language $\mathcal {L}$ . Let $T_0$ be a reduct of T. Let $\mathcal {L}_S = \mathcal {L}\cup \{S\}$ , for S a new unary predicate symbol, and $T_S$ be the $\mathcal {L}_S$ -theory that axiomatises the following structures: $(\mathscr {M},\mathscr {M}_0)$ consist of a model $\mathscr {M}$ of T and S is a predicate for a model $\mathscr {M}_0$ of $T_0$ which is a substructure of $\mathscr {M}$ . We present a setting for the existence of a model-companion $TS$ of $T_S$ . As a consequence, we obtain the existence of the model-companion of the following theories, for $p>0$ a prime number: • $\mathrm {ACF}_p$ , $\mathrm {SCF}_{e,p}$ , $\mathrm {Psf}_p$ , $\mathrm {ACFA}_p$ , $\mathrm {ACVF}_{p,p}$ in appropriate languages expanded by arbitrarily many predicates for additive subgroups;• $\mathrm {ACF}_p$ , $\mathrm {ACF}_0$ in the language of rings expanded by a single predicate for a multiplicative subgroup;• $\mathrm {PAC}_p$ -fields, in an appropriate language expanded by arbitrarily many predicates for additive subgroups.From an independence relation in T, we define independence relations in $TS$ and identify which properties of are transferred to those new independence relations in $TS$ , and under which conditions. This allows us to exhibit hypotheses under which the expansion from T to $TS$ preserves $\mathrm {NSOP}_{1}$ , simplicity, or stability. In particular, under some technical hypothesis on T, we may draw the following picture (the left column implies the right column): Configuration $T_0\subseteq T$ Generic expansion $TS$ $T_0 = T$ Preserves stability $T_0\subseteq T$ Preserves $\mathrm {NSOP}_{1}$ $T_0 = \emptyset $ Preserves simplicityIn particular, this construction produces new examples of $\mathrm {NSOP}_{1}$ not simple theories, and we study in depth a particular example: the expansion of an algebraically closed field of positive characteristic by a generic additive subgroup. We give a full description of imaginaries, forking, and Kim-forking in this example.The second part studies expansions of the group of integers by p-adic valuations. We prove quantifier elimination in a natural language and compute the dp-rank of these expansions: it equals the number of independent p-adic valuations considered. Thus, the expansion of the integers by one p-adic valuation is a new dp-minimal expansion of the group of integers. Finally, we prove that the latter expansion does not admit intermediate structures: any definable set in the expansion is either definable in the group structure or is able to “reconstruct” the valuation using only the group operation.Abstract prepared by Christian d’Elbée.E-mail: delbee@math.univ-lyon1.frURL: https://choum.net/~chris/page_perso

Interpolating bit-vector formulas using uninterpreted predicates and Presburger arithmetic

The inference of program invariants over machine arithmetic, commonly called bit-vector arithmetic, is an important problem in verification. Techniques that have been successful for unbounded arithmetic, in particular Craig interpolation, have turned out to be difficult to generalise to machine arithmetic: existing bit-vector interpolation approaches are based either on eager translation from bit-vectors to unbounded arithmetic, resulting in complicated constraints that are hard to solve and interpolate, or on bit-blasting to propositional logic, in the process losing all arithmetic structure. We present a new approach to bit-vector interpolation, as well as bit-vector quantifier elimination (QE), that works by lazy translation of bit-vector constraints to unbounded arithmetic. Laziness enables us to fully utilise the information available during proof search (implied by decisions and propagation) in the encoding, and this way produce constraints that can be handled relatively easily by existing interpolation and QE procedures for Presburger arithmetic. The lazy encoding is complemented with a set of native proof rules for bit-vector equations and non-linear (polynomial) constraints, this way minimising the number of cases a solver has to consider. We also incorporate a method for handling concatenations and extractions of bit-vector efficiently.

An optimal quantum error-correcting procedure using quantifier elimination

Quantum communication channels suffer from various noises, which are mathematically modeled by error super-operators. To combat these errors, it is necessary to design recovery super-operators. We aim to construct the optimal recovery that maximizes the minimum fidelity through the noisy channel. It is typically a MAX–MIN problem, out of the scope of convex optimization. Compared to existing methods, our method is exact and complete by a reduction to quantifier elimination over real closed fields in a fragment of two alternative quantifier blocks. Finally, the complexity is shown to be in EXP.

Algorithmic properties of some fragments of concatenation theory

The paper considers two fragments of the word theory with concatenation. The first fragment has two relations denoting that one of the words is a prefix (respectively, a suffix) of another one. It is proved that this theory is algorithmically equivalent to elementary arithmetic and, therefore, undecidable. The second fragment has a countable set of power operations. It is proved that this theory admits effective quantifier elimination and is, therefore, decidable.

Bounds for Elimination of Unknowns in Systems of Differential-Algebraic Equations

Abstract Elimination of unknowns in systems of equations, starting with Gaussian elimination, is a problem of general interest. The problem of finding an a priori upper bound for the number of differentiations in elimination of unknowns in a system of differential-algebraic equations (DAEs) is an important challenge, going back to Ritt (1932). The first characterization of this via an asymptotic analysis is due to Grigoriev’s result (1989) on quantifier elimination in differential fields, but the challenge still remained. In this paper, we present a new bound, which is a major improvement over the previously known results. We also present a new lower bound, which shows asymptotic tightness of our upper bound in low dimensions, which are frequently occurring in applications. Finally, we discuss applications of our results to designing new algorithms for elimination of unknowns in systems of DAEs.

Quantifier elimination for quasi-real closed fields

We prove quantifier elimination for the theory of quasi-real closed fields with a compatible valuation. This unifies the same known results for algebraically closed valued fields and real closed valued fields.

The theories of Baldwin–Shi hypergraphs and their atomic models

We show that the quantifier elimination result for the Shelah-Spencer almost sure theories of sparse random graphs $$G(n,n^{-\alpha })$$ given by Laskowski (Isr J Math 161:157–186, 2007) extends to their various analogues. The analogues will be obtained as theories of generic structures of certain classes of finite structures with a notion of strong substructure induced by rank functions and we will call the generics Baldwin–Shi hypergraphs. In the process we give a method of constructing extensions whose ‘relative rank’ is negative but arbitrarily small in context. We give a necessary and sufficient condition for the theory of a Baldwin–Shi hypergraph to have atomic models. We further show that for certain well behaved classes of theories of Baldwin–Shi hypergraphs, the existentially closed models and the atomic models correspond.

Quantifier elimination theory and maps which preserve semipositivity

We give an algorithm determining whether a hermiticity-preserving superoperator is positive. In our approach we apply techniques of quantifier elimination theory for real numbers. Furthermore, we argue that quantifier elimination theory should play more significant role in quantum information theory and other areas as well.

Complexity of linear relaxations in integer programming

For a set X of integer points in a polyhedron, the smallest number of facets of any polyhedron whose set of integer points coincides with X is called the relaxation complexity {{,mathrm{rc},}}(X). This parameter, introduced by Kaibel & Weltge (2015), captures the complexity of linear descriptions of X without using auxiliary variables. Using tools from combinatorics, geometry of numbers, and quantifier elimination, we make progress on several open questions regarding {{,mathrm{rc},}}(X) and its variant {{,mathrm{rc},}}_mathbb {Q}(X), restricting the descriptions of X to rational polyhedra. As our main results we show that {{,mathrm{rc},}}(X) = {{,mathrm{rc},}}_mathbb {Q}(X) when: (a) X is at most four-dimensional, (b) X represents every residue class in (mathbb {Z}/2mathbb {Z})^d, (c) the convex hull of X contains an interior integer point, or (d) the lattice-width of X is above a certain threshold. Additionally, {{,mathrm{rc},}}(X) can be algorithmically computed when X is at most three-dimensional, or X satisfies one of the conditions (b), (c), or (d) above. Moreover, we obtain an improved lower bound on {{,mathrm{rc},}}(X) in terms of the dimension of X.

Algebraic Stability Analysis of Particle Swarm Optimization Using Stochastic Lyapunov Functions and Quantifier Elimination

This paper adds to the discussion about theoretical aspects of particle swarm stability by proposing to employ stochastic Lyapunov functions and to determine the convergence set by quantifier elimination. We present a computational procedure and show that this approach leads to a reevaluation and extension of previously known stability regions for PSO using a Lyapunov approach under stagnation assumptions.

Formal Calculation of Positive Invariant Sets for the Lorenz Family Combining Lyapunov Approaches and Quantifier Elimination

AbstractThe Lorenz family is a class of dynamic systems which is parameterized in one variable and includes both the classic Lorenz system and the Chen system. Both systems (and therefore the Lorenz family) can show chaotic behaviour. For different questions of system analysis, e.g. for the estimation of various types of dimensions, it is helpful to be able to determine bounds on the attractor. One typical approach ist the usage of Lyapunov functions to describe positive invariant sets. However, this approach usually requires a good knowledge of the system to perform the necessary calculations. For polynomial systems, these calculations can be carried out using a computation technique known as quantifier elimination. In this contribution we describe this approach and employ it to calculate bounds on the Lorenz family.

A proof of Bel’tyukov-Lipshitz theorem by quasi-quantifier elimination. I. Definitions and GCD-lemma

This paper is the first part of a new proof of decidability of the existential theory of the structure , where | corresponds to the binary divisibility relation. The decidability was proved independently in 1976 by A. P. Bel’tyukov and L. Lipshitz. In 1977, V.I. Mart’yanov proved an equivalent result by considering the ternary GCD predicate instead of divisibility (the predicates are interchangeable with respect to existential definability). Generalizing in some sense the notion of quantifier elimination (QE) algorithm, we construct a quasi-QE algorithm to prove decidability of the positive existential theory of the structure <...>. We reduce to the decision problem for this theory the decision problem for the existential theory of the structure <...>. A quasi-QE algorithm, which performs this reduction, will be constructed in the second part of the proof. Transformations of formulas are based on a generalization of the Chinese remainder theorem to systems of the form GCD(ai, bi +x) = di for every i [1..m], where ai, bi, di are some integers such that ai 6 = 0, di > 0.

On maps which preserve semipositivity and quantifier elimination theory for real numbers

Assume that [Formula: see text] is a superoperator which preserves hermiticity. We give an algorithm determining whether [Formula: see text] preserves semipositivity (we call [Formula: see text] positive in this case). Our approach to the problem has a model-theoretic nature, namely, we apply techniques of quantifier elimination theory for real numbers. An approach based on these techniques seems to be the only one that allows to decide whether an arbitrary hermiticity-preserving [Formula: see text] is positive. Before we go to detailed analysis of the problem, we argue that quantifier elimination for real numbers (and also for complex numbers) can play a significant role in quantum information theory and other areas as well.

Model theory of R-trees

We show the theory of pointed $\R$-trees with radius at most $r$ is axiomatizable in a suitable continuous signature. We identify the model companion $\rbRT_r$ of this theory and study its properties. In particular, the model companion is complete and has quantifier elimination; it is stable but not superstable. We identify its independence relation and find built-in canonical bases for non-algebraic types. Among the models of $\rbRT_r$ are $\R$-trees that arise naturally in geometric group theory. In every infinite cardinal, we construct the maximum possible number of pairwise non-isomorphic models of $\rbRT_r$; indeed, the models we construct are pairwise non-homeomorphic. We give detailed information about the type spaces of $\rbRT_r$. Among other things, we show that the space of $2$-types over the empty set is nonseparable. Also, we characterize the principal types of finite tuples (over the empty set) and use this information to conclude that $\rbRT_r$ has no atomic model.