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First‐order undefinability of the notion of transfinitely uplifting cardinals Math. Logic Q. (IF 0.244) Pub Date : 2021-04-03 Kentaro Fujimoto
Audrito and Viale introduced the new large cardinal notion of an (α)‐uplifting cardinal (for an ordinal α). We shall show that this notion cannot be defined (or expressed) in the standard first‐order language of set theory for every tranfinite α.
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Varieties of pseudocomplemented Kleene algebras Math. Logic Q. (IF 0.244) Pub Date : 2021-04-01 Diego Castaño, Valeria Castaño, José Patricio Díaz Varela, Marcela Muñoz Santis
In this paper we study the subdirectly irreducible algebras in the variety PCD M of pseudocomplemented De Morgan algebras by means of their De Morgan p‐spaces. We introduce the notion of the body of an algebra L ∈ PCD M and determine Body ( L ) when L is subdirectly irreducible. As a consequence of this, in the case of pseudocomplemented Kleene algebras, two special subvarieties arise naturally, for
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A fixed point theory over stratified truth Math. Logic Q. (IF 0.244) Pub Date : 2021-01-15 Andrea Cantini
We present a theory of stratified truth ST μ with a μ‐operator, where terms representing fixed points of stratified monotone operations are available. We prove that ST μ is relatively intepretable into Quine's NF (or subsystems thereof). The motivation is to investigate a strong theory of truth, which is consistent by means of stratification, i.e., by adopting an implicit type theoretic discipline
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On universal modules with pure embeddings Math. Logic Q. (IF 0.244) Pub Date : 2021-01-15 Thomas G. Kucera, Marcos Mazari‐Armida
We show that certain classes of modules have universal models with respect to pure embeddings: Let R be a ring, T a first‐order theory with an infinite model extending the theory of R‐modules and K T = ( Mod ( T ) , ≤ pp ) (where ⩽pp stands for “pure submodule”). Assume K T has the joint embedding and amalgamation properties. If λ | T | = λ or ∀ μ < λ ( μ | T | < λ ) , then K T has a universal model
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A note on chain‐based semi‐Heyting algebras Math. Logic Q. (IF 0.244) Pub Date : 2021-01-16 Juan Manuel Cornejo, Luiz F. Monteiro, Hanamantagouda P. Sankappanavar, Ignacio D. Viglizzo
We determine the number of non‐isomorphic semi‐Heyting algebras on an n‐element chain, where n is a positive integer, using a recursive method. We then prove that the numbers obtained agree with those determined in [1]. We apply the formula to calculate the number of non‐isomorphic semi‐Heyting chains of a given size in some important subvarieties of the variety of semi‐Heyting algebras that were introduced
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Special subsets of the generalized Cantor space and generalized Baire space Math. Logic Q. (IF 0.244) Pub Date : 2021-01-17 Michał Korch, Tomasz Weiss
In this paper, we are interested in parallels to the classical notions of special subsets in R defined in the generalized Cantor and Baire spaces (2κ and κ κ ). We consider generalizations of the well‐known classes of special subsets, like Lusin sets, strongly null sets, concentrated sets, perfectly meagre sets, σ‐sets, γ‐sets, sets with the Menger, the Rothberger, or the Hurewicz property, but also
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On the completeness and the decidability of strictly monadic second‐order logic Math. Logic Q. (IF 0.244) Pub Date : 2021-01-15 Kento Takagi, Ryo Kashima
Regarding strictly monadic second‐order logic (SMSOL), which is the fragment of monadic second‐order logic in which all predicate constants are unary and there are no function symbols, we show that a standard deductive system with full comprehension is sound and complete with respect to standard semantics. This result is achieved by showing that in the case of SMSOL, the truth value of any formula
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Agreement reducibility Math. Logic Q. (IF 0.244) Pub Date : 2021-01-15 Rachel Epstein, Karen Lange
We introduce agreement reducibility and highlight its major features. Given subsets A and B of N , we write A ≤ agree B if there is a total computable function f : N → N satisfying for all e , e ′ , W e ∩ A = W e ′ ∩ A if and only if W f ( e ) ∩ B = W f ( e ′ ) ∩ B .
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Surjectively rigid chains Math. Logic Q. (IF 0.244) Pub Date : 2021-01-13 Mayra Montalvo‐Ballesteros, John K. Truss
We study rigidity properties of linearly ordered sets (chains) under automorphisms, embeddings, epimorphisms, and endomorphisms. We focus on two main cases: dense subchains of the real numbers, and uncountable dense chains of higher regular cardinalities. We also give a Fraenkel‐Mostowski model which illustrates the role of the axiom of choice in one of the key proofs.
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What is effective transfinite recursion in reverse mathematics? Math. Logic Q. (IF 0.244) Pub Date : 2021-01-17 Anton Freund
In the context of reverse mathematics, effective transfinite recursion refers to a principle that allows us to construct sequences of sets by recursion along arbitrary well orders, provided that each set is Δ 1 0 ‐definable relative to the previous stages of the recursion. It is known that this principle is provable in ACA 0 . In the present note, we argue that a common formulation of effective transfinite
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Decidable variables for constructive logics Math. Logic Q. (IF 0.244) Pub Date : 2021-01-16 Satoru Niki
Ishihara's problem of decidable variables asks which class of decidable propositional variables is sufficient to warrant classical theorems in intuitionistic logic. We present several refinements to the class proposed by Ishii for this problem, which also allows the class to cover Glivenko's logic. We also treat the extension of the problem to minimal logic, suggesting a couple of new classes.
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Remarks on Gitik's model and symmetric extensions on products of the Lévy collapse Math. Logic Q. (IF 0.244) Pub Date : 2020-10-01 Amitayu Banerjee
We improve on results and constructions by Apter, Dimitriou, Gitik, Hayut, Karagila, and Koepke concerning large cardinals, ultrafilters, and cofinalities without the axiom of choice. In particular, we show the consistency of the following statements from certain assumptions: the first supercompact cardinal can be the first uncountable regular cardinal, all successors of regular cardinals are Ramsey
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The Hanf number in the strictly stable case Math. Logic Q. (IF 0.244) Pub Date : 2020-09-29 Saharon Shelah
We associate Hanf numbers H ( t ) to triples t = ( T , T 1 , p ) where T and T1 are theories and p is a type. We show that the Hanf number for the property: “there is a model M1 of T 1 which omits p, but M 1 ↾ τ is saturated” is larger than the Hanf number of L λ + , κ but smaller than the Hanf number of L ( 2 λ ) + , κ when T is stable with κ = κ ( T ) . In fact, surprisingly, we even characterise
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Strategic equivalence among hat puzzles of various protocols with many colors Math. Logic Q. (IF 0.244) Pub Date : 2020-09-15 Masaru Kada, Souji Shizuma
We discuss puzzles of prisoners and hats with infinitely many prisoners and more than two hat colors. Assuming that the set of hat colors is equipped with a commutative group structure, we prove strategic equivalence among puzzles of several protocols with countably many prisoners.
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A note on the finitization of Abelian and Tauberian theorems Math. Logic Q. (IF 0.244) Pub Date : 2020-09-28 Thomas Powell
We present finitary formulations of two well known results concerning infinite series, namely Abel's theorem, which establishes that if a series converges to some limit then its Abel sum converges to the same limit, and Tauber's theorem, which presents a simple condition under which the converse holds. Our approach is inspired by proof theory, and in particular Gödel's functional interpretation, which
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Independent families of functions and permutations Math. Logic Q. (IF 0.244) Pub Date : 2020-09-15 Nattapon Sonpanow, Pimpen Vejjajiva
We study independent families of functions and permutations and associated cardinal characteristics i f and i p . In this paper, we show that these cardinals lie between the cardinals p and i and give some related consistency results.
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Existential definability of modal frame classes Math. Logic Q. (IF 0.244) Pub Date : 2020-09-18 Tin Perkov, Luka Mikec
We prove an existential analogue of the Goldblatt‐Thomason Theorem which characterizes modal definability of elementary classes of Kripke frames using closure under model theoretic constructions. The less known version of the Goldblatt‐Thomason Theorem gives general conditions, without the assumption of first‐order definability, but uses non‐standard constructions and algebraic semantics. We present
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A note on ordinal exponentiation and derivatives of normal functions Math. Logic Q. (IF 0.244) Pub Date : 2020-09-28 Anton Freund
Michael Rathjen and the present author have shown that Π 1 1 ‐bar induction is equivalent to (a suitable formalization of) the statement that every normal function has a derivative, provably in ACA 0 . In this note we show that the base theory can be weakened to RCA 0 . Our argument makes crucial use of a normal function f with f ( α ) ≤ 1 + α 2 and f ′ ( α ) = ω ω α . We shall also exhibit a normal
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A note on the non‐forking‐instances topology Math. Logic Q. (IF 0.244) Pub Date : 2020-09-28 Ziv Shami
The non‐forking‐instances topology (NFI topology) is a topology on the Stone space of a theory T that depends on a reduct T − of T. This topology has been used in [6] to describe the set of universal transducers for ( T , T − ) (invariants sets that translate forking‐open sets in T − to forking‐open sets in T). In this paper we show that in contrast to the stable case, the NFI topology need not be
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Word problems and ceers Math. Logic Q. (IF 0.244) Pub Date : 2020-09-28 Valentino Delle Rose, Luca San Mauro, Andrea Sorbi
This note addresses the issue as to which ceers can be realized by word problems of computably enumerable (or, simply, c.e.) structures (such as c.e. semigroups, groups, and rings), where being realized means to fall in the same reducibility degree (under the notion of reducibility for equivalence relations usually called “computable reducibility”), or in the same isomorphism type (with the isomorphism
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Russell's typicality as another randomness notion Math. Logic Q. (IF 0.244) Pub Date : 2020-09-21 Athanassios Tzouvaras
We reformulate slightly Russell's notion of typicality, so as to eliminate its circularity and make it applicable to elements of any first‐order structure. We argue that the notion parallels Martin‐Löf (ML) randomness, in the sense that it uses definable sets in place of computable ones and sets of “small” cardinality (i.e., strictly smaller than that of the structure domain) in place of measure zero
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Nonstandard methods for finite structures Math. Logic Q. (IF 0.244) Pub Date : 2020-09-18 Akito Tsuboi
We discuss the possibility of applying the compactness theorem to the study of finite structures. Given a class of finite structures, it is important to determine whether it can be expressed by a particular category of sentences. We are interested in this type of problem, and use nonstandard method for showing the non‐expressibility of certain classes of finite graphs by an existential monadic second
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Orders on computable rings Math. Logic Q. (IF 0.244) Pub Date : 2020-07-12 Huishan Wu
The Artin‐Schreier theorem says that every formally real field has orders. Friedman, Simpson and Smith showed in [6] that the Artin‐Schreier theorem is equivalent to WKL 0 over RCA 0 . We first prove that the generalization of the Artin‐Schreier theorem to noncommutative rings is equivalent to WKL 0 over RCA 0 . In the theory of orderings on rings, following an idea of Serre, we often show the existence
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More on trees and Cohen reals Math. Logic Q. (IF 0.244) Pub Date : 2020-07-02 Giorgio Laguzzi, Brendan Stuber‐Rousselle
In this paper we analyse some questions concerning trees on κ, both for the countable and the uncountable case, and the connections with Cohen reals. In particular, we provide a proof for one of the implications left open in [6, Question 5.2] about the diagram for regularity properties.
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Stability, the NIP, and the NSOP: model theoretic properties of formulas via topological properties of function spaces Math. Logic Q. (IF 0.244) Pub Date : 2020-07-01 Karim Khanaki
We study and characterize stability, the negation of the independence property (NIP) and the negation of the strict order property (NSOP) in terms of topological and measure theoretical properties of classes of functions. We study a measure theoretic property, Talagrand's stability, and explain the relationship between this property and the NIP in continuous logic. Using a result of Bourgain, Fremlin
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The classification of countable models of set theory Math. Logic Q. (IF 0.244) Pub Date : 2020-06-29 John Clemens, Samuel Coskey, Samuel Dworetzky
We study the complexity of the classification problem for countable models of set theory ( ZFC ). We prove that the classification of arbitrary countable models of ZFC is Borel complete, meaning that it is as complex as it can conceivably be. We then give partial results concerning the classification of countable well‐founded models of ZFC .
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Axiomatizing first order consequences in inclusion logic Math. Logic Q. (IF 0.244) Pub Date : 2020-06-23 Fan Yang
Inclusion logic is a variant of dependence logic that was shown to have the same expressive power as positive greatest fixed‐point logic. Inclusion logic is not axiomatisable in full, but its first order consequences can be axiomatized. In this paper, we provide such an explicit partial axiomatization by introducing a system of natural deduction for inclusion logic that is sound and complete for first
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The Cichoń diagram for degrees of relative constructibility Math. Logic Q. (IF 0.244) Pub Date : 2020-06-23 Corey Bacal Switzer
Following a line of research initiated in [4], we describe a general framework for turning reduction concepts of relative computability into diagrams forming an analogy with the Cichoń diagram for cardinal characteristics of the continuum. We show that working from relatively modest assumptions about a notion of reduction, one can construct a robust version of such a diagram. As an application, we
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The choice property in tame expansions of o‐minimal structures Math. Logic Q. (IF 0.244) Pub Date : 2020-06-23 Pantelis E. Eleftheriou, Ayhan Günaydın, Philipp Hieronymi
We establish the choice property, a weak analogue of definable choice, for certain tame expansions of o‐minimal structures. Most noteworthily, this property holds for dense pairs of real closed fields, as well as for expansions of o‐minimal structures by a dense independent set.
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Singly generated quasivarieties and residuated structures Math. Logic Q. (IF 0.244) Pub Date : 2020-06-21 Tommaso Moraschini, James G. Raftery, Johann J. Wannenburg
A quasivariety K of algebras has the joint embedding property (JEP) if and only if it is generated by a single algebra A. It is structurally complete if and only if the free ℵ0‐generated algebra in K can serve as A. A consequence of this demand, called ‘passive structural completeness’ (PSC), is that the nontrivial members of K all satisfy the same existential positive sentences. We prove that if K
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A game‐theoretic proof of Shelah's theorem on labeled trees Math. Logic Q. (IF 0.244) Pub Date : 2020-06-16 Trevor M. Wilson
We give a new proof of a theorem of Shelah which states that for every family of labeled trees, if the cardinality κ of the family is much larger (in the sense of large cardinals) than the cardinality λ of the set of labels, more precisely if the partition relation κ → ( ω ) λ < ω holds, then there is a homomorphism from one labeled tree in the family to another. Our proof uses a characterization of
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Turing invariant sets and the perfect set property Math. Logic Q. (IF 0.244) Pub Date : 2020-06-14 Clovis Hamel, Haim Horowitz, Saharon Shelah
We show that ZF + DC + “all Turing invariant sets of reals have the perfect set property” implies that all sets of reals have the perfect set property. We also show that this result generalizes to all countable analytic equivalence relations.
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On a strengthening of Jónssonness for ℵω Math. Logic Q. (IF 0.244) Pub Date : 2020-06-14 Monroe Eskew
We discuss a system of strengthenings of “ ℵ ω is Jónsson” indexed by real numbers, and identify a strongest one. We give a proof of a theorem of Silver and show that there is a barrier to weakening its hypothesis.
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Editorial Math. Logic Q. (IF 0.244) Pub Date : 2020-04-02
Dear readers of Mathematical Logic Quarterly: Dr Hugo Nobrega has been the Editorial Assistant of our journal for four years, from 2016 to 2019, and has now handed over to his successor, Dr Thomas Piecha from the Eberhard Karls Universität Tübingen, who started to work for the journal on New Year's Day 2020. We thank Hugo for four years of excellent service for the journal and welcome Thomas as our
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The torsion‐free part of the Ziegler spectrum of orders over Dedekind domains Math. Logic Q. (IF 0.244) Pub Date : 2020-03-24 Lorna Gregory, Sonia L'Innocente, Carlo Toffalori
We study the R‐torsion‐free part of the Ziegler spectrum of an order Λ over a Dedekind domain R. We underline and comment on the role of lattices over Λ. We describe the torsion‐free part of the spectrum when Λ is of finite lattice representation type.
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Computability of graphs Math. Logic Q. (IF 0.244) Pub Date : 2020-03-19 Zvonko Iljazović
We consider topological pairs ( A , B ) , B ⊆ A , which have computable type, which means that they have the following property: if X is a computable topological space and f : A → X a topological imbedding such that f ( A ) and f ( B ) are semicomputable sets in X, then f ( A ) is a computable set in X. It is known, e.g., that ( M , ∂ M ) has computable type if M is a compact manifold with boundary
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On the Herbrand functional interpretation Math. Logic Q. (IF 0.244) Pub Date : 2020-03-16 Paulo Oliva, Chuangjie Xu
We show that the types of the witnesses in the Herbrand functional interpretation can be simplified, avoiding the use of “sets of functionals” in the interpretation of implication and universal quantification. This is done by presenting an alternative formulation of the Herbrand functional interpretation, which we show to be equivalent to the original presentation. As a result of this investigation
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Local weak presaturation of the strongly non‐stationary ideal Math. Logic Q. (IF 0.244) Pub Date : 2020-03-16 Masahiro Shioya, Naoki Yamaura
We give a model of set theory in which the strongly non‐stationary ideal over ℘ μ μ is weakly presaturated below some canonical set. Here μ is a regular uncountable cardinal. The model is the forcing extension with the Lévy collapse of a Woodin cardinal to the successor of μ. This improves on results of Goldring and of the first author.
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Lowness for isomorphism, countable ideals, and computable traceability Math. Logic Q. (IF 0.244) Pub Date : 2020-03-16 Johanna N. Y. Franklin, Reed Solomon
We show that every countable ideal of degrees that are low for isomorphism is contained in a principal ideal of degrees that are low for isomorphism by adapting an exact pair construction. We further show that within the hyperimmune free degrees, lowness for isomorphism is entirely independent of computable traceability.
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On weak square, approachability, the tree property, and failures of SCH in a choiceless context Math. Logic Q. (IF 0.244) Pub Date : 2020-03-16 Arthur W. Apter
We show that the consistency of the theories ZF + ¬ AC ω + “ GCH holds below ℵ ω ” + “there is an injection f : ℵ ω + 2 → ℘ ( ℵ ω ) ” + “both □ ℵ ω ∗ and AP ℵ ω fail” and ZF + ¬ AC ω + “ GCH holds below ℵ ω ” + “there is an injection f : ℵ ω + 2 → ℘ ( ℵ ω ) ” + “ ℵ ω + 1 satisfies the tree property” follow from the appropriate supercompactness hypotheses. These provide answers in a choiceless context
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Expansions of the p‐adic numbers that interpret the ring of integers Math. Logic Q. (IF 0.244) Pub Date : 2020-03-11 Nathanaël Mariaule
Let Q p ∼ be the field of p‐adic numbers in the language of rings. In this paper we consider the theory of Q p ∼ expanded by two predicates interpreted by multiplicative subgroups α Z and β Z where α , β ∈ N are multiplicatively independent. We show that the theory of this structure interprets Peano arithmetic if α and β have positive p‐adic valuation. If either α or β has zero valuation we show that
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Cohen forcing and inner models Math. Logic Q. (IF 0.244) Pub Date : 2020-03-09 Jonas Reitz
Given an inner model W ⊂ V and a regular cardinal κ, we consider two alternatives for adding a subset to κ by forcing: the Cohen poset Add(κ, 1), and the Cohen poset of the inner model Add ( κ , 1 ) W . The forcing from W will be at least as strong as the forcing from V (in the sense that forcing with the former adds a generic for the latter) if and only if the two posets have the same cardinality
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On p‐adic semi‐algebraic continuous selections Math. Logic Q. (IF 0.244) Pub Date : 2020-02-25 Athipat Thamrongthanyalak
Let E ⊆ Q p n and T be a set‐valued map from E to Q p m . We prove that if T is p‐adic semi‐algebraic, lower semi‐continuous and T ( x ) is closed for every x ∈ E , then T has a p‐adic semi‐algebraic continuous selection. In addition, we include three applications of this result. The first one is related to Fefferman's and Kollár's question on existence of p‐adic semi‐algebraic continuous solution
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A two‐dimensional metric temporal logic Math. Logic Q. (IF 0.244) Pub Date : 2019-12-26 Stefano Baratella, Andrea Masini
We introduce a two‐dimensional metric (interval) temporal logic whose internal and external time flows are dense linear orderings. We provide a suitable semantics and a sequent calculus with axioms for equality and extralogical axioms. Then we prove completeness and a semantic partial cut elimination theorem down to formulas of a certain type.
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New substitution bases for complexity classes Math. Logic Q. (IF 0.244) Pub Date : 2019-12-23 Stefano Mazzanti
The set AC 0 ( F ) , the AC 0 closure of F, is the closure with respect to substitution and concatenation recursion on notation of a set of basic functions comprehending the set F. By improving earlier work, we show that AC 0 ( F ) is the substitution closure of a simple function set and characterize well‐known function complexity classes as the substitution closure of finite sets of simple functions
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Inner mantles and iterated HOD Math. Logic Q. (IF 0.244) Pub Date : 2019-12-17 Jonas Reitz, Kameryn J. Williams
We present a class forcing notion M ( η ) , uniformly definable for ordinals η, which forces the ground model to be the ηth inner mantle of the extension, in which the sequence of inner mantles has length at least η. This answers a conjecture of Fuchs, Hamkins, and Reitz [1] in the positive. We also show that M ( η ) forces the ground model to be the ηth iterated HOD of the extension, where the sequence
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The small‐is‐very‐small principle Math. Logic Q. (IF 0.244) Pub Date : 2019-12-16 Albert Visser
The central result of this paper is the small‐is‐very‐small principle for restricted sequential theories. The principle says roughly that whenever the given theory shows that a definable property has a small witness, i.e., a witness in a sufficiently small definable cut, then it shows that the property has a very small witness: i.e., a witness below a given standard number. Which cuts are sufficiently
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Ultrafilter extensions do not preserve elementary equivalence Math. Logic Q. (IF 0.244) Pub Date : 2019-12-16 Denis I. Saveliev, Saharon Shelah
We show that there are models M 1 and M 2 such that M 1 elementarily embeds into M 2 but their ultrafilter extensions β β ( M 1 ) and β β ( M 2 ) are not elementarily equivalent.
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Complete Lω1,ω‐sentences with maximal models in multiple cardinalities Math. Logic Q. (IF 0.244) Pub Date : 2019-12-13 John Baldwin, Ioannis Souldatos
In [5], examples of incomplete sentences are given with maximal models in more than one cardinality. The question was raised whether one can find similar examples of complete sentences. In this paper, we give examples of complete L ω 1 , ω ‐sentences with maximal models in more than one cardinality. From (homogeneous) characterizability of κ we construct sentences with maximal models in κ and in one
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When does every definable nonempty set have a definable element? Math. Logic Q. (IF 0.244) Pub Date : 2019-12-12 François G. Dorais, Joel David Hamkins
The assertion that every definable set has a definable element is equivalent over ZF to the principle V = HOD , and indeed, we prove, so is the assertion merely that every Π2‐definable set has an ordinal‐definable element. Meanwhile, every model of ZFC has a forcing extension satisfying V ≠ HOD in which every Σ2‐definable set has an ordinal‐definable element. Similar results hold for HOD ( R ) and
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Concrete barriers to quantifier elimination in finite dimensional C*‐algebras Math. Logic Q. (IF 0.244) Pub Date : 2019-12-12 Christopher J. Eagle, Todd Schmid
Work of Eagle, Farah, Goldbring, Kirchberg, and Vignati shows that the only separable C*‐algebras that admit quantifier elimination in continuous logic are C , C 2 , M 2 ( C ) , and the continuous functions on the Cantor set. We show that, among finite dimensional C*‐algebras, quantifier elimination does hold if the language is expanded to include two new predicate symbols: One for minimal projections
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Pseudo‐c‐archimedean and pseudo‐finite cyclically ordered groups Math. Logic Q. (IF 0.244) Pub Date : 2019-12-11 Gérard Leloup
Robinson and Zakon gave necessary and sufficient conditions for an abelian ordered group to satisfy the same first‐order sentences as an archimedean abelian ordered group (i.e., which embeds in the group of real numbers). The present paper generalizes their work to obtain similar results for infinite subgroups of the group of unimodular complex numbers. Furthermore, the groups which satisfy the same
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Generalised pseudointersections Math. Logic Q. (IF 0.244) Pub Date : 2019-12-05 Jonathan Schilhan
This paper is a compilation of results originating in the author's master thesis. We give a useful characterization of the generalized bounding and dominating numbers, b ( κ ) and d ( κ ) . We show that t ( κ ) ≤ add ( M κ ) when κ = κ < κ . And we prove a higher analogue of Bell's theorem stating that p = c is equivalent to MA ( σ ‐centered).
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Model completion of scaled lattices and co‐Heyting algebras of p‐adic semi‐algebraic sets Math. Logic Q. (IF 0.244) Pub Date : 2019-10-21 Luck Darnière
Let p be prime number, K be a p‐adically closed field, X ⊆ K m a semi‐algebraic set defined over K and L ( X ) the lattice of semi‐algebraic subsets of X which are closed in X. We prove that the complete theory of L ( X ) eliminates quantifiers in a certain language L ASC , the L ASC ‐structure on L ( X ) being an extension by definition of the lattice structure. Moreover it is decidable, contrary
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Π11‐Martin‐Löf randomness and Π11‐Solovay completeness Math. Logic Q. (IF 0.244) Pub Date : 2019-10-17 Claude Sureson
Developing an analogue of Solovay reducibility in the higher recursion setting, we show that results from the classical computably enumerable case can be extended to the new context.
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The axiom of determinacy implies dependent choice in mice Math. Logic Q. (IF 0.244) Pub Date : 2019-10-14 Sandra Müller
We show that the Axiom of Dependent Choice, DC , holds in countably iterable, passive premice M constructed over their reals which satisfy the Axiom of Determinacy, AD , in a ZF + DC R M background universe. This generalizes an argument of Kechris for L ( R ) using Steel's analysis of scales in mice. In particular, we show that for any n ≤ ω and any countable set of reals A so that M n ( A ) ∩ R =
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Degrees of categoricity of trees and the isomorphism problem Math. Logic Q. (IF 0.244) Pub Date : 2019-10-13 Mohammad Assem Mahmoud
In this paper, we show that for any computable ordinal α, there exists a computable tree of rank α + 1 with strong degree of categoricity 0 ( 2 α ) if α is finite, and with strong degree of categoricity 0 ( 2 α + 1 ) if α is infinite. In fact, these are the greatest possible degrees of categoricity for such trees. For a computable limit ordinal α, we show that there is a computable tree of rank α with
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Nonstandard characterisations of tensor products and monads in the theory of ultrafilters Math. Logic Q. (IF 0.244) Pub Date : 2019-10-07 Lorenzo Luperi Baglini
We use nonstandard methods, based on iterated hyperextensions, to develop applications to Ramsey theory of the theory of monads of ultrafilters. This is performed by studying in detail arbitrary tensor products of ultrafilters, as well as by characterising their combinatorial properties by means of their monads. This extends to arbitrary sets and properties methods previously used to study partition
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Definable topological dynamics for trigonalizable algebraic groups over Qp Math. Logic Q. (IF 0.244) Pub Date : 2019-10-07 Ningyuan Yao
We study the flow ( G ( Q p ) , S G ( Q p ) ) of trigonalizable algebraic group acting on its type space, focusing on the problem raised in [17] of whether weakly generic types coincide with almost periodic types if the group has global definable f‐generic types, equivalently whether the union of minimal subflows of a suitable type space is closed. We shall give a description of f‐generic types of
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Łoś's theorem and the axiom of choice Math. Logic Q. (IF 0.244) Pub Date : 2019-09-30 Eleftherios Tachtsis
In set theory without the Axiom of Choice ( AC ), we investigate the problem of the placement of Łoś's Theorem ( LT ) in the hierarchy of weak choice principles, and answer several open questions from the book Consequences of the Axiom of Choice by Howard and Rubin, as well as an open question by Brunner. We prove a number of results summarised in § 3.
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