On a problem of MacDowell and Specker

The article investigates the classification with precision up to equivalence of involutions in the algebra of upper triangular matrices over the ring of integers of algebraic numbers of quadratic fields.The description of involutions in algebras represents one of the classical problems of ring theory. Standard examples of involutions are transposition in matrix algebra and conjugation in the field of complex numbers and the algebra of quaternions.In the case where the field 𝑃 has a characteristic different from two, a complete description of involutions with precision up to their equivalence in the algebra 𝑇𝑛(𝑃) for any natural number 𝑛 was obtained in [15]. In this work [3] involutions in the algebra of upper triangular matrices over commutative rings are studied. If the ring is a field of characteristic 2 or a Boolean ring, then necessary and sufficient conditions for the finiteness of the number of equivalence classesof involutions were found.This article is a continuation of the work of [3]. In the article [3], in particular, the number of equivalence classes of involutions in the algebras of upper triangular matrices over the ring of integers was found. In this regard, the natural result is the problem of describing involutions with precision up to their equivalence in algebras of upper triangular matrices over the ring of algebraic integers of quadratic fields, to which this work is devoted. In the work, the number of equivalence classes of involutions in such algebras is found and the method of finding representatives in each equivalence class is illustrated with examples. Upon receipt the main results in this work, the apparatus of the theory of Pell’s equations is significantly used.

We study hierarchies of validity problems for prefix fragments in probability logic with quantifiers over propositional formulas, denoted $ \mathcal{Q}\mathcal{P}\mathcal{L} $ , and its versions. It is proved that if a subfield $ \mathfrak{F} $ of reals is definable in the standard model of arithmetic by a secondorder formula without set quantifiers, then the validity problem over $ \mathfrak{F} $ -valued probability structures for Σ4- $ \mathcal{Q}\mathcal{P}\mathcal{L} $ -sentences is Π1 1 -complete; as a consequence, the corresponding hierarchy of validity problems collapses. Moreover, in proving this fact, we state that an ∃∀-theory of Presburger arithmetic with a single free unary predicate is Π1 1 -complete, which generalizes a well-known result of Halpern relating to the entire theory mentioned.

Unlike the paradoxicality of the strengthened Liar sentence, the paradoxicality of this infinite list of ‘Yablo sentences’ is not at all straightforward. In Ketland (forthcoming), it is shown that the list of Yablo sentences is not formally inconsistent. More precisely, the list of ‘Yablo biconditionals’ (all instances of ‘Yn m > n, Ym is not true’) is not inconsistent with the relevant local disquotation principle (all instances of ‘Yn is true Yn’). Rather, the combination is w-inconsistent. Furthermore, with an appropriate definition of the extension of ‘true’, it is possible to satisfy this combination on any non-standard model of arithmetic.1 So, in a sense, Yablo’s paradox is not a genuine paradox. Rather, it is an ‘w-paradox’, an infinite set of sentences which is unsatisfiable on the standard model of arithmetic.

Lower bounds are established on the computational complexity of the decision problem and on the inherent lengths of proofs for two classical decidable theories of logic: the first-order theory of the real numbers under addition, and Presburger arithmetic — the first-order theory of addition on the natural numbers. There is a fixed constant c > 0 such that for every (nondeterministic) decision procedure for determining the truth of sentences of real addition and for all sufficiently large n, there is a sentence of length n for which the decision procedure runs for more than 2cn steps. In the case of Presburger arithmetic, the corresponding bound is \({2^{{2^{cn}}}}\). These bounds apply also to the minimal lengths of proofs for any complete axiomatization in which the axioms are easily recognized.KeywordsDecision ProcedureFinite Abelian GroupScanning HeadBinary WordReal AdditionThese 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.

Lagrange’s four squares theorem is a classical result in number theory. Recently, Z.-W. Sun found that it can be further refined in various ways. In this paper we study some conjectures of Sun and obtain various refinements of Lagrange’s theorem. We show

Max–min of polynomials and exponential diophantine equations

Let K be an algebraic number field with non-trivial class group G and OK be its ring of integers. For k 2 N and some real x 1, let Fk(x) denote the number of non-zero principal ideals aOK with norm bounded by x such that a has at most k distinct factorizations into irreducible elements. It is well known that Fk(x) behaves, for x ! 1, asymptotically like x(logx) 1/|G| 1 (loglogx) Nk(G) . In this article, it is proved that for every prime p, N1(Cp Cp) = 2p, and it is also proved that N1(Cmp Cmp) = 2mp if N1(Cm Cm) = 2m and m is large enough. In particular, it is shown that for each positive integer n there is a positive integer m such that N1(Cmn Cmn) = 2mn. Our results confirm a conjecture given by W. Narkiewicz thirty years ago partly and improve the known results substantially.

Power integral bases in prime-power cyclotomic fields

This paper deals with model-checking of fragments and extensions of CTL* on infinite-state Presburger counter systems, where the states are vectors of integers and the transitions are determined by means of relations definable within Presburger arithmetic. We have identified a natural class of admissible counter systems (ACS) for which we show that the quantification over paths in CTL* can be simulated by quantification over tuples of natural numbers, eventually allowing translation of the whole Presburger-CTL* into Presburger arithmetic, thereby enabling effective model checking. We have provided evidence that our results are close to optimal with respect to the class of counter systems described above. Finally, we design a complete semi-algorithm to verify first-order LTL properties over trace-flattable counter systems, extending the previous underlying FAST semi-algorithm to verify reachability questions over flattable counter systems.KeywordsModel CheckTemporal LogicAtomic FormulaCounter SystemSymbolic Model CheckThese 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.

Infinitary Methods in the Model Theory of Set Theory

The aim of this paper is to extend the Bass-Milnor-Serre theorem to the nonstandard rings associated with nonstandard models of Peano arithmetic, in brief to Peano rings.First, we recall the classical setting. Let k be an algebraïc number field, and let θ be its ring of integers. Let n be an integer ≥ 3, and let G be the group Sln(θ) of (n, n) matrices of determinant 1 with coefficients in θ.The profinite topology in G is the topology having as fundamental system of open subgroups the subgroups of finite index.Congruence subgroups of finite index of G are the kernels of the maps Sln(θ) → Sln(θ/I) for which all ideals I of θ are of finite index. By taking these subgroups as a fundamental system of open subgroups, one obtains the congruence topology on G. Every open set for this topology is open in the profinite topology.We denote by Ḡ (resp., Ĝ) the completion of G for the congruence (resp., profinite) topology.The Bass-Milnor-Serre theorem [1] consists of the two following statements:(A) If k admits a real embedding, then we have an exact sequenceThat is, Ĝ and Ḡ are isomorphic.(B) If k is totally imaginary, then one has an exact sequencewhere μ(k)is the group of the roots of unity of k.

CHAPTER 2 - NUMBERS FOR PROFIT AND LOSS AND NUMBERS FOR SHARING

Let $n$ and $m$ be positive integers such that $n<m$. In this paper we compute the density of rectangular unimodular $n \times m$ matrices over the ring of algebraic integers of a number field.

Introduction Around 1900 Hilbert, Hecke ([7]), Blumenthal ([2]) and others started the study of certain 2-dimensional complex spaces, which are closely related to the classification of special types of 2-dimensional abelian varieties. These complex spaces can easily be described. In fact, let n be a natural number, n > 1, which is square free and let K = Q q/n). Then, if o K is the ring of algebraic integers of K, the group SLz(oK) operates in a natural way on ~ • ~ and on ~ • ~ where ~ is the upper and ~ the lower half plane of C. The quotients of See • ~ and Jg x J g by the action of SL2(ov,) are the 2-dimensional complex spaces mentioned above. If the field K has a unit of negative norm, then the two actions on ~ • ~ and ~ • J g are isomorphic. This is true if n is a prime congruent 1 rood 4, the only case we shall consider in this paper. Therefore, from now on we assume that K= Q (l,/p), where p is a prime congruent 1 mod 4. The complex space Jg x .)~/SLz(oK) can be compactified by means of a finite number of points, called the cusps, to a compact 2-dimensional complex space. After resolving the cusps and also the quotient singularities on ~ x ~ / S L 2 (OK) , both in a canonical, explicit way, a nonsingular compact complex surface Y(R) is obtained, which in fact is an algebraic surface. The field of meromorphic (i. e. rational) functions on Y(p) is isomorphic to the field of meromorphic functions of • ~ / S L 2 (OK). On the other hand, although no complete classification of algebraic surfaces is known, there exists a rough classification in several classes (for most of which the surfaces contained in that class can be classified completely, at least in principle). In big outline this classification was already known to the italian school, but its precise formulation (this time also covering the non-algebraic case) and many of the proofs involved are due to Kodaira. Now the question considered in this paper is the following: where are the surfaces Y(p) to be placed in the rough classification of algebraic surfaces?

Some covering and packing results in number theory