Cardinal functions on ultra products of Boolean algebras

1997 ◽  
Vol 62 (1) ◽  
pp. 43-59 ◽  
Author(s):  
Douglas Peterson
Keyword(s):  
Boolean Algebra ◽  
Cardinal Number ◽  
Boolean Algebras ◽  
Open Problems ◽  
Cardinal Functions ◽  
Image Position

This article is concerned with functions k assigning a cardinal number to each infinite Boolean algebra (BA), and the behaviour of such functions under ultraproducts. For some common functions k we havefor others we have ≤ instead, under suitable assumptions. For the function π character we go into more detail. More specifically, ≥ holds when F is regular, for cellularity, length, irredundance, spread, and incomparability. ≤ holds for π. ≥ holds under GCH for F regular, for depth, π, πχ, χ, h-cof, tightness, hL, and hd. These results show that ≥ can consistently hold in ZFC since if V = L holds then all uniform ultrafilters are regular. For π-character we prove two more results: (1) If F is regular and ess , then(2) It is relatively consistent to have , where A is the denumerable atomless BA.A thorough analysis of what happens without the assumption that F is regular can be found in Rosłanowski, Shelah [8] and Magidor, Shelah [5]. Those papers also mention open problems concerning the above two possible inequalities.

On the Representation of Boolean Algebras

1962 ◽  
Vol 5 (1) ◽  
pp. 37-41 ◽  
Author(s):  
Günter Bruns
Keyword(s):  
Boolean Algebra ◽  
Boolean Algebras ◽  
Two Systems ◽  
Image Position

Let B be a Boolean algebra and let ℳ and n be two systems of subsets of B, both containing all finite subsets of B. Let us assume further that the join ∨M of every set M∊ℳ and the meet ∧N of every set N∊n exist. Several authors have treated the question under which conditions there exists an isomorphism φ between B and a field δ of sets, satisfying the conditions:

A Generalization of Certain Rings of A. L. Foster

1963 ◽  
Vol 6 (1) ◽  
pp. 55-60 ◽  
Author(s):  
Adil Yaqub
Keyword(s):  
Boolean Algebra ◽  
Boolean Algebras ◽  
Boolean Ring ◽  
Boolean Rings ◽  
Image Position

The concept of a Boolean ring, as a ring A in which every element is idempotent (i. e., a2 = a for all a in A), was first introduced by Stone [4]. Boolean algebras and Boolean rings, though historically and conceptually different, were shown by Stone to be equationally interdefinable. Indeed, let (A, +, x) be a Boolean ring with unit 1, and let (A, ∪, ∩, ') be a Boolean algebra, where ∩, ∪, ', denote "union", " intersection", and "complement". The equations which convert the Boolean ring into a Boolean algebra are:IConversely, the equations which convert the Boolean algebra into a Boolean ring are:II

Games played on Boolean algebras

1983 ◽  
Vol 48 (3) ◽  
pp. 714-723 ◽  
Author(s):  
Matthew Foreman
Keyword(s):  
Boolean Algebra ◽  
Topological Space ◽  
Closed Subset ◽  
Winning Strategy ◽  
Boolean Algebras ◽  
Algebra Structure ◽  
Partial Converse ◽  
Image Position ◽  
Special Case

In this paper we consider the special case of the Banach-Mazur game played on a topological space when the space also has an underlying Boolean Algebra structure. This case was first studied by Jech [2]. The version of the Banach-Mazur game we will play is the following game played on the Boolean algebra:Players I and II alternate moves playing a descending sequence of elements of a Boolean algebra ℬ.Player II wins the game iff Πi∈ωbi ≠ 0. Jech first considered these games and showed:Theorem (Jech [2]). ℬ is (ω1, ∞)-distributive iff player I does not have a winning strategy in the game played on ℬ.If ℬ has a dense ω-closed subset then it is easy to see that player II has a winning strategy in this game. This paper establishes a partial converse to this, namely it gives cardinality conditions on ℬ under which II having a winning strategy implies ω-closure.In the course of proving the converse, we consider games of length > ω and generalize Jech's theorem to these games. Finally we present an example due to C. Gray that stands in counterpoint to the theorems in this paper.In this section we give a few basis definitions and explain our notation. These definitions are all standard.

Locally Flat Vector Lattices

1980 ◽  
Vol 32 (4) ◽  
pp. 924-936 ◽  
Author(s):  
Marlow Anderson
Keyword(s):  
Boolean Algebra ◽  
Essential Extension ◽  
Boolean Algebras ◽  
Complete Boolean Algebra ◽  
Lattice Ordered Group ◽  
Ordered Group ◽  
Vector Lattices ◽  
Trivial Intersection ◽  
Image Position

Let G be a lattice-ordered group (l-group). If X ⊆ G, then letThen X’ is a convex l-subgroup of G called a polar. The set P(G) of all polars of G is a complete Boolean algebra with ‘ as complementation and set-theoretic intersection as meet. An l-subgroup H of G is large in G (G is an essential extension of H) if each non-zero convex l-subgroup of G has non-trivial intersection with H. If these l-groups are archimedean, it is enough to require that each non-zero polar of G meets H. This implies that the Boolean algebras of polars of G and H are isomorphic. If K is a cardinal summand of G, then K is a polar, and we write G = K⊞K'.

Equational bases of boolean algebras

1964 ◽  
Vol 29 (3) ◽  
pp. 115-124 ◽  
Author(s):  
F. M. Sioson
Keyword(s):  
Boolean Algebra ◽  
Algebraic System ◽  
Boolean Algebras ◽  
Definition Of ◽  
Image Position

It is well-known that a Boolean algebra (B, +, ., ‐) may be defined as an algebraic system with at least two elements such that (for all x, y, z ε B): These axioms or equations are not independent, in the sense that some of them are logical consequences of the others. B. A. Bernstein [1] thought that the first three and their duals form an independent dual-symmetric definition of a Boolean algebra, but R. Montague and J. Tarski [3] proved later that B1 (or B̅1) follows from B2, B3, B̅1, B̅2, B̅3 (from B1, B2, B3, B̅2, B̅3).

On the compactness of some Boolean algebras

1984 ◽  
Vol 49 (1) ◽  
pp. 63-67
Author(s):  
Jacek Cichoń
Keyword(s):  
Boolean Algebra ◽  
Continuum Hypothesis ◽  
Cardinal Number ◽  
Boolean Algebras ◽  
Cardinal Numbers ◽  
Martin’S Axiom ◽  
Reduced Products ◽  
Standard Set ◽  
General Continuum ◽  
The Continuum

We say that the Boolean algebra B is λ-compact, where λ is a cardinal number, if for every family Z ⊆ B∖{0} of power at most λ, if inf Z = 0 then for some finite subfamily Z0 ⊆ Z we have inf Z0 = 0.On the set of all finite subsets of a cardinal number κ, which is denoted [κ]<ω, the sets of the form for any p Є [κ]<ω generate the filter Tκ.This filter is a standard example of a κ-regular filter (see [2]). Because of the importance of κ-regular filters in studying the saturatedness of ultraproducts and reduced products by model-theoretic methods, the question of compactness of the algebra Bκ = P([κ]<ω/Tκ was natural. This question in the most optimistical way was formulated by M. Benda [1, Problem 5c]: is the algebra Bκω-compact for every uncountable κ?In this paper we show that for most of the cardinal numbers which are greater or equal to 2ω the algebra Bκ is not ω-compact. Hence, in view of obtained results, the following question appears: does there exist an uncountable κ such that the algebra Bκ is κ-compact?We use standard set-theoretical notations. CH denotes the Continuum Hypothesis, GCH denotes the General Continuum Hypothesis and MA denotes Martin's Axiom.

Subgroups of a free group and the axiom of choice

1985 ◽  
Vol 50 (2) ◽  
pp. 458-467 ◽  
Author(s):  
Paul E. Howard
Keyword(s):  
Free Group ◽  
Cardinal Number ◽  
Cyclic Permutation ◽  
Axiom Of Choice ◽  
Embedding Theorem ◽  
Open Problems ◽  
Power Set ◽  
Partial List ◽  
Image Position ◽  
The Axiom Of Choice

Nielsen [7] has proved that every subgroup of a free group of finite rank is free. The theorem was later strengthened by Schreier [8] by eliminating the finiteness restriction on the rank. Several proofs of this theorem (known as the Nielsen-Schreier theorem, henceforth denoted by NS) have appeared since Schreier's 1927 paper (see [1] and [2]). All proofs of NS use the axiom of choice (AC) and it is natural to ask whether NS is equivalent to AC. Läuchli has given a partial answer to this question by proving [6] that the negation of NS is consistent with ZFA (Zermelo-Fraenkel set theory weakened to permit the existence of atoms). By the Jech-Sochor embedding theorem (see [3] and [4]) ZFA can be replaced by ZF. Some form of AC, therefore, is needed to prove NS. The main purpose of this paper is to give a further answer to this question.In §2 we prove that NS implies ACffin (the axiom of choice for sets of finite sets). In §3 we show that a strengthened version of NS implies AC and in §4 we give a partial list of open problems.Let y be a set; ∣y∣ denotes the cardinal number of y and (y) is the power set of y. If p is a permutation of y and t ∈ y, the p-orbit of t is the set {pn(t): n is an integer}. Ifwe call p a cyclic permutation of y. If f is a function with domain y and x ⊆ y, f″x denotes the set {f(t):t ∈ x}. If A is a subset of a group (G, °) (sometimes (G, °) will be denoted by G) then A−1 = {x−1:x ∈ A} and [A] denotes the subgroup of G generated by A.

scholarly journals CHOICE-FREE STONE DUALITY

2019 ◽  
Vol 85 (1) ◽  
pp. 109-148
Author(s):  
NICK BEZHANISHVILI ◽  
WESLEY H. HOLLIDAY
Keyword(s):  
Boolean Algebra ◽  
Boolean Algebras ◽  
Stone Space ◽  
Spectral Space ◽  
Topological Representation ◽  
Stone Duality ◽  
Closed Sets ◽  
Spectral Spaces ◽  
Basic Facts ◽  
Regular Open

AbstractThe standard topological representation of a Boolean algebra via the clopen sets of a Stone space requires a nonconstructive choice principle, equivalent to the Boolean Prime Ideal Theorem. In this article, we describe a choice-free topological representation of Boolean algebras. This representation uses a subclass of the spectral spaces that Stone used in his representation of distributive lattices via compact open sets. It also takes advantage of Tarski’s observation that the regular open sets of any topological space form a Boolean algebra. We prove without choice principles that any Boolean algebra arises from a special spectral space X via the compact regular open sets of X; these sets may also be described as those that are both compact open in X and regular open in the upset topology of the specialization order of X, allowing one to apply to an arbitrary Boolean algebra simple reasoning about regular opens of a separative poset. Our representation is therefore a mix of Stone and Tarski, with the two connected by Vietoris: the relevant spectral spaces also arise as the hyperspace of nonempty closed sets of a Stone space endowed with the upper Vietoris topology. This connection makes clear the relation between our point-set topological approach to choice-free Stone duality, which may be called the hyperspace approach, and a point-free approach to choice-free Stone duality using Stone locales. Unlike Stone’s representation of Boolean algebras via Stone spaces, our choice-free topological representation of Boolean algebras does not show that every Boolean algebra can be represented as a field of sets; but like Stone’s representation, it provides the benefit of a topological perspective on Boolean algebras, only now without choice. In addition to representation, we establish a choice-free dual equivalence between the category of Boolean algebras with Boolean homomorphisms and a subcategory of the category of spectral spaces with spectral maps. We show how this duality can be used to prove some basic facts about Boolean algebras.

scholarly journals On primes not dividing binomial coefficients

1993 ◽  
Vol 113 (2) ◽  
pp. 225-232 ◽  
Author(s):  
J. W. Sander
Keyword(s):  
Binomial Coefficients ◽  
Open Problems ◽  
Image Position

AbstractWe prove thatthus dealing with open problems concerning divisors of binomial coefficients.

On the elementary equivalence of automorphism groups of Boolean algebras; downward Skolem Löwenheim theorems and compactness of related quantifiers

1980 ◽  
Vol 45 (2) ◽  
pp. 265-283 ◽  
Author(s):  
Matatyahu Rubin ◽  
Saharon Shelah
Keyword(s):  
Boolean Algebra ◽  
Automorphism Groups ◽  
Order Logic ◽  
Boolean Algebras ◽  
First Order Logic ◽  
Elementary Equivalence ◽  
First Order ◽  
Finite Models ◽  
Countably Compact

AbstractTheorem 1. (◊ℵ1,) If B is an infinite Boolean algebra (BA), then there is B1, such that ∣ Aut (B1) ≤∣B1∣ = ℵ1 and 〈B1, Aut (B1)〉 ≡ 〈B, Aut(B)〉.Theorem 2. (◊ℵ1) There is a countably compact logic stronger than first-order logic even on finite models.This partially answers a question of H. Friedman. These theorems appear in §§1 and 2.Theorem 3. (a) (◊ℵ1) If B is an atomic ℵ-saturated infinite BA, Ψ Є Lω1ω and 〈B, Aut (B)〉 ⊨Ψ then there is B1, Such that ∣Aut(B1)∣ ≤ ∣B1∣ =ℵ1, and 〈B1, Aut(B1)〉⊨Ψ. In particular if B is 1-homogeneous so is B1. (b) (a) holds for B = P(ω) even if we assume only CH.

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