Cardinal Invariants Concerning Functions Whose Sum Is Almost Continuous Krzysztof Ciesielski West Virginia University, [email protected]
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Set Theory, by Thomas Jech, Academic Press, New York, 1978, Xii + 621 Pp., '$53.00
BOOK REVIEWS 775 BULLETIN (New Series) OF THE AMERICAN MATHEMATICAL SOCIETY Volume 3, Number 1, July 1980 © 1980 American Mathematical Society 0002-9904/80/0000-0 319/$01.75 Set theory, by Thomas Jech, Academic Press, New York, 1978, xii + 621 pp., '$53.00. "General set theory is pretty trivial stuff really" (Halmos; see [H, p. vi]). At least, with the hindsight afforded by Cantor, Zermelo, and others, it is pretty trivial to do the following. First, write down a list of axioms about sets and membership, enunciating some "obviously true" set-theoretic principles; the most popular Hst today is called ZFC (the Zermelo-Fraenkel axioms with the axiom of Choice). Next, explain how, from ZFC, one may derive all of conventional mathematics, including the general theory of transfinite cardi nals and ordinals. This "trivial" part of set theory is well covered in standard texts, such as [E] or [H]. Jech's book is an introduction to the "nontrivial" part. Now, nontrivial set theory may be roughly divided into two general areas. The first area, classical set theory, is a direct outgrowth of Cantor's work. Cantor set down the basic properties of cardinal numbers. In particular, he showed that if K is a cardinal number, then 2", or exp(/c), is a cardinal strictly larger than K (if A is a set of size K, 2* is the cardinality of the family of all subsets of A). Now starting with a cardinal K, we may form larger cardinals exp(ic), exp2(ic) = exp(exp(fc)), exp3(ic) = exp(exp2(ic)), and in fact this may be continued through the transfinite to form expa(»c) for every ordinal number a. -
Mathematics 144 Set Theory Fall 2012 Version
MATHEMATICS 144 SET THEORY FALL 2012 VERSION Table of Contents I. General considerations.……………………………………………………………………………………………………….1 1. Overview of the course…………………………………………………………………………………………………1 2. Historical background and motivation………………………………………………………….………………4 3. Selected problems………………………………………………………………………………………………………13 I I. Basic concepts. ………………………………………………………………………………………………………………….15 1. Topics from logic…………………………………………………………………………………………………………16 2. Notation and first steps………………………………………………………………………………………………26 3. Simple examples…………………………………………………………………………………………………………30 I I I. Constructions in set theory.………………………………………………………………………………..……….34 1. Boolean algebra operations.……………………………………………………………………………………….34 2. Ordered pairs and Cartesian products……………………………………………………………………… ….40 3. Larger constructions………………………………………………………………………………………………..….42 4. A convenient assumption………………………………………………………………………………………… ….45 I V. Relations and functions ……………………………………………………………………………………………….49 1.Binary relations………………………………………………………………………………………………………… ….49 2. Partial and linear orderings……………………………..………………………………………………… ………… 56 3. Functions…………………………………………………………………………………………………………… ….…….. 61 4. Composite and inverse function.…………………………………………………………………………… …….. 70 5. Constructions involving functions ………………………………………………………………………… ……… 77 6. Order types……………………………………………………………………………………………………… …………… 80 i V. Number systems and set theory …………………………………………………………………………………. 84 1. The Natural Numbers and Integers…………………………………………………………………………….83 2. Finite induction -
Biography Paper – Georg Cantor
Mike Garkie Math 4010 – History of Math UCD Denver 4/1/08 Biography Paper – Georg Cantor Few mathematicians are house-hold names; perhaps only Newton and Euclid would qualify. But there is a second tier of mathematicians, those whose names might not be familiar, but whose discoveries are part of everyday math. Examples here are Napier with logarithms, Cauchy with limits and Georg Cantor (1845 – 1918) with sets. In fact, those who superficially familier with Georg Cantor probably have two impressions of the man: First, as a consequence of thinking about sets, Cantor developed a theory of the actual infinite. And second, that Cantor was a troubled genius, crippled by Freudian conflict and mental illness. The first impression is fundamentally true. Cantor almost single-handedly overturned the Aristotle’s concept of the potential infinite by developing the concept of transfinite numbers. And, even though Bolzano and Frege made significant contributions, “Set theory … is the creation of one person, Georg Cantor.” [4] The second impression is mostly false. Cantor certainly did suffer from mental illness later in his life, but the other emotional baggage assigned to him is mostly due his early biographers, particularly the infamous E.T. Bell in Men Of Mathematics [7]. In the racially charged atmosphere of 1930’s Europe, the sensational story mathematician who turned the idea of infinity on its head and went crazy in the process, probably make for good reading. The drama of the controversy over Cantor’s ideas only added spice. 1 Fortunately, modern scholars have corrected the errors and biases in older biographies. -
641 1. P. Erdös and A. H. Stone, Some Remarks on Almost Periodic
1946] DENSITY CHARACTERS 641 BIBLIOGRAPHY 1. P. Erdös and A. H. Stone, Some remarks on almost periodic transformations, Bull. Amer. Math. Soc. vol. 51 (1945) pp. 126-130. 2. W. H. Gottschalk, Powers of homeomorphisms with almost periodic propertiesf Bull. Amer. Math. Soc. vol. 50 (1944) pp. 222-227. UNIVERSITY OF PENNSYLVANIA AND UNIVERSITY OF VIRGINIA A REMARK ON DENSITY CHARACTERS EDWIN HEWITT1 Let X be an arbitrary topological space satisfying the TVseparation axiom [l, Chap. 1, §4, p. 58].2 We recall the following definition [3, p. 329]. DEFINITION 1. The least cardinal number of a dense subset of the space X is said to be the density character of X. It is denoted by the symbol %{X). We denote the cardinal number of a set A by | A |. Pospisil has pointed out [4] that if X is a Hausdorff space, then (1) |X| g 22SW. This inequality is easily established. Let D be a dense subset of the Hausdorff space X such that \D\ =S(-X'). For an arbitrary point pÇ^X and an arbitrary complete neighborhood system Vp at p, let Vp be the family of all sets UC\D, where U^VP. Thus to every point of X, a certain family of subsets of D is assigned. Since X is a Haus dorff space, VpT^Vq whenever p j*£q, and the correspondence assigning each point p to the family <DP is one-to-one. Since X is in one-to-one correspondence with a sub-hierarchy of the hierarchy of all families of subsets of D, the inequality (1) follows. -
SRB MEASURES for ALMOST AXIOM a DIFFEOMORPHISMS José Alves, Renaud Leplaideur
SRB MEASURES FOR ALMOST AXIOM A DIFFEOMORPHISMS José Alves, Renaud Leplaideur To cite this version: José Alves, Renaud Leplaideur. SRB MEASURES FOR ALMOST AXIOM A DIFFEOMORPHISMS. 2013. hal-00778407 HAL Id: hal-00778407 https://hal.archives-ouvertes.fr/hal-00778407 Preprint submitted on 20 Jan 2013 HAL is a multi-disciplinary open access L’archive ouverte pluridisciplinaire HAL, est archive for the deposit and dissemination of sci- destinée au dépôt et à la diffusion de documents entific research documents, whether they are pub- scientifiques de niveau recherche, publiés ou non, lished or not. The documents may come from émanant des établissements d’enseignement et de teaching and research institutions in France or recherche français ou étrangers, des laboratoires abroad, or from public or private research centers. publics ou privés. SRB MEASURES FOR ALMOST AXIOM A DIFFEOMORPHISMS JOSE´ F. ALVES AND RENAUD LEPLAIDEUR Abstract. We consider a diffeomorphism f of a compact manifold M which is Almost Axiom A, i.e. f is hyperbolic in a neighborhood of some compact f-invariant set, except in some singular set of neutral points. We prove that if there exists some f-invariant set of hyperbolic points with positive unstable-Lebesgue measure such that for every point in this set the stable and unstable leaves are \long enough", then f admits a probability SRB measure. Contents 1. Introduction 2 1.1. Background 2 1.2. Statement of results 2 1.3. Overview 4 2. Markov rectangles 5 2.1. Neighborhood of critical zone 5 2.2. First generation of rectangles 6 2.3. Second generation rectangles 7 2.4. -
Bounding, Splitting and Almost Disjointness
Bounding, splitting and almost disjointness Jonathan Schilhan Advisor: Vera Fischer Kurt G¨odelResearch Center Fakult¨atf¨urMathematik, Universit¨atWien Abstract This bachelor thesis provides an introduction to set theory, cardinal character- istics of the continuum and the generalized cardinal characteristics on arbitrary regular cardinals. It covers the well known ZFC relations of the bounding, the dominating, the almost disjointness and the splitting number as well as some more recent results about their generalizations to regular uncountable cardinals. We also present an overview on the currently known consistency results and formulate open questions. 1 CONTENTS Contents Introduction 3 1 Prerequisites 5 1.1 Model Theory/Predicate Logic . .5 1.2 Ordinals/Cardinals . .6 1.2.1 Ordinals . .7 1.2.2 Cardinals . .9 1.2.3 Regular Cardinals . 10 2 Cardinal Characteristics of the continuum 11 2.1 The bounding and the dominating number . 11 2.2 Splitting and mad families . 13 3 Cardinal Characteristics on regular uncountable cardinals 16 3.1 Generalized bounding, splitting and almost disjointness . 16 3.2 An unexpected inequality between the bounding and splitting numbers . 18 3.2.1 Elementary Submodels . 18 3.2.2 Filters and Ideals . 19 3.2.3 Proof of Theorem 3.2.1 (s(κ) ≤ b(κ)) . 20 3.3 A relation between generalized dominating and mad families . 23 References 28 2 Introduction @0 Since it was proven that the continuum hypothesis (2 = @1) is independent of the axioms of ZFC, the natural question arises what value 2@0 could take and it was shown @0 that 2 could be consistently nearly anything. -
Almost-Free E-Rings of Cardinality ℵ1 Rudige¨ R Gob¨ El, Saharon Shelah and Lutz Strung¨ Mann
Sh:785 Canad. J. Math. Vol. 55 (4), 2003 pp. 750–765 Almost-Free E-Rings of Cardinality @1 Rudige¨ r Gob¨ el, Saharon Shelah and Lutz Strung¨ mann Abstract. An E-ring is a unital ring R such that every endomorphism of the underlying abelian group R+ is multiplication by some ring element. The existence of almost-free E-rings of cardinality greater @ than 2 0 is undecidable in ZFC. While they exist in Godel'¨ s universe, they do not exist in other models @ of set theory. For a regular cardinal @1 ≤ λ ≤ 2 0 we construct E-rings of cardinality λ in ZFC which have @1-free additive structure. For λ = @1 we therefore obtain the existence of almost-free E-rings of cardinality @1 in ZFC. 1 Introduction + Recall that a unital ring R is an E-ring if the evaluation map ": EndZ(R ) ! R given by ' 7! '(1) is a bijection. Thus every endomorphism of the abelian group R+ is multiplication by some element r 2 R. E-rings were introduced by Schultz [20] and easy examples are subrings of the rationals Q or pure subrings of the ring of p-adic integers. Schultz characterized E-rings of finite rank and the books by Feigelstock [9, 10] and an article [18] survey the results obtained in the eighties, see also [8, 19]. In a natural way the notion of E-rings extends to modules by calling a left R-module M an E(R)-module or just E-module if HomZ(R; M) = HomR(R; M) holds, see [1]. -
The Axiom of Choice and Its Implications
THE AXIOM OF CHOICE AND ITS IMPLICATIONS KEVIN BARNUM Abstract. In this paper we will look at the Axiom of Choice and some of the various implications it has. These implications include a number of equivalent statements, and also some less accepted ideas. The proofs discussed will give us an idea of why the Axiom of Choice is so powerful, but also so controversial. Contents 1. Introduction 1 2. The Axiom of Choice and Its Equivalents 1 2.1. The Axiom of Choice and its Well-known Equivalents 1 2.2. Some Other Less Well-known Equivalents of the Axiom of Choice 3 3. Applications of the Axiom of Choice 5 3.1. Equivalence Between The Axiom of Choice and the Claim that Every Vector Space has a Basis 5 3.2. Some More Applications of the Axiom of Choice 6 4. Controversial Results 10 Acknowledgments 11 References 11 1. Introduction The Axiom of Choice states that for any family of nonempty disjoint sets, there exists a set that consists of exactly one element from each element of the family. It seems strange at first that such an innocuous sounding idea can be so powerful and controversial, but it certainly is both. To understand why, we will start by looking at some statements that are equivalent to the axiom of choice. Many of these equivalences are very useful, and we devote much time to one, namely, that every vector space has a basis. We go on from there to see a few more applications of the Axiom of Choice and its equivalents, and finish by looking at some of the reasons why the Axiom of Choice is so controversial. -
Georg Cantor English Version
GEORG CANTOR (March 3, 1845 – January 6, 1918) by HEINZ KLAUS STRICK, Germany There is hardly another mathematician whose reputation among his contemporary colleagues reflected such a wide disparity of opinion: for some, GEORG FERDINAND LUDWIG PHILIPP CANTOR was a corruptor of youth (KRONECKER), while for others, he was an exceptionally gifted mathematical researcher (DAVID HILBERT 1925: Let no one be allowed to drive us from the paradise that CANTOR created for us.) GEORG CANTOR’s father was a successful merchant and stockbroker in St. Petersburg, where he lived with his family, which included six children, in the large German colony until he was forced by ill health to move to the milder climate of Germany. In Russia, GEORG was instructed by private tutors. He then attended secondary schools in Wiesbaden and Darmstadt. After he had completed his schooling with excellent grades, particularly in mathematics, his father acceded to his son’s request to pursue mathematical studies in Zurich. GEORG CANTOR could equally well have chosen a career as a violinist, in which case he would have continued the tradition of his two grandmothers, both of whom were active as respected professional musicians in St. Petersburg. When in 1863 his father died, CANTOR transferred to Berlin, where he attended lectures by KARL WEIERSTRASS, ERNST EDUARD KUMMER, and LEOPOLD KRONECKER. On completing his doctorate in 1867 with a dissertation on a topic in number theory, CANTOR did not obtain a permanent academic position. He taught for a while at a girls’ school and at an institution for training teachers, all the while working on his habilitation thesis, which led to a teaching position at the university in Halle. -
Elements of Set Theory
Elements of set theory April 1, 2014 ii Contents 1 Zermelo{Fraenkel axiomatization 1 1.1 Historical context . 1 1.2 The language of the theory . 3 1.3 The most basic axioms . 4 1.4 Axiom of Infinity . 4 1.5 Axiom schema of Comprehension . 5 1.6 Functions . 6 1.7 Axiom of Choice . 7 1.8 Axiom schema of Replacement . 9 1.9 Axiom of Regularity . 9 2 Basic notions 11 2.1 Transitive sets . 11 2.2 Von Neumann's natural numbers . 11 2.3 Finite and infinite sets . 15 2.4 Cardinality . 17 2.5 Countable and uncountable sets . 19 3 Ordinals 21 3.1 Basic definitions . 21 3.2 Transfinite induction and recursion . 25 3.3 Applications with choice . 26 3.4 Applications without choice . 29 3.5 Cardinal numbers . 31 4 Descriptive set theory 35 4.1 Rational and real numbers . 35 4.2 Topological spaces . 37 4.3 Polish spaces . 39 4.4 Borel sets . 43 4.5 Analytic sets . 46 4.6 Lebesgue's mistake . 48 iii iv CONTENTS 5 Formal logic 51 5.1 Propositional logic . 51 5.1.1 Propositional logic: syntax . 51 5.1.2 Propositional logic: semantics . 52 5.1.3 Propositional logic: completeness . 53 5.2 First order logic . 56 5.2.1 First order logic: syntax . 56 5.2.2 First order logic: semantics . 59 5.2.3 Completeness theorem . 60 6 Model theory 67 6.1 Basic notions . 67 6.2 Ultraproducts and nonstandard analysis . 68 6.3 Quantifier elimination and the real closed fields . -
Almost-At-A-Distance-Accepted
Almost at-a-distance Andrew McKenzie (Kansas) and Lydia Newkirk (Rutgers) accepted draft in Linguistics & Philosophy [email protected] [email protected] https://doi.org/10.1007/s10988-019-09275-6 Abstract We claim that the meaning of the adverbial almost contains both a scalar proximity measure and a modal that allows it to work sometimes when proximity fails, what we call the at-a-distance reading. Essentially, almost can hold if the proposition follows from the normal uninterrupted out- comes of adding a small enough number of premises to a selection of rel- evant facts. Almost at-a-distance is blocked when the temporal properties of the topic time and Davidsonian event prevent normal outcomes from coming true when they need to. This approach to almost differs from the two general approaches that have emerged in the literature, by replacing the negative polar condition (not p) with a positive antecedent condition that entails not p while avoid- ing the numerous well-documented complications of employing a polar condition. Since this approach to almost involves a circumstantial base with a non-interrupting ordering source, almost behaves in certain ways like the progressive, and shows contextual variability of the same kinds that we see with premise sets. 1 Introduction The adverbial almost has a clear intuitive meaning, but has proven very difficult to reconcile with a formal semantics. Two basic approaches characterize our understanding of almost in the literature. Under scalar alternative accounts, almost p holds when p is false but some close alternative proposition q is true. Modal closeness accounts argue that almost p holds of world w when p is false in w, but true in some close alternative world w0. -
21 Cardinal and Ordinal Numbers. by W. Sierpióski. Monografie Mate
BOOK REVIEWS 21 Cardinal and ordinal numbers. By W. Sierpióski. Monografie Mate- matyczne, vol. 34. Warszawa, Panstwowe Wydawnictwo Naukowe, 1958. 487 pp. Not since the publication in 1928 of his Leçons sur les nombres transfinis has Sierpióski written a book on transfinite numbers. The present book, embodying the fruits of a lifetime of research and ex perience in teaching the subject, is therefore most welcome. Although generally similar in outline to the earlier work, it is an entirely new book, and more than twice as long. The exposition is leisurely and thickly interspersed with illuminating discussion and examples. The result is a book which is highly instructive and eminently readable. Whether one takes the chapters in order or dips in at random he is almost sure to find something interesting. Many examples and ap plications are included in the form of exercises, nearly all accom panied by solutions. The exposition is from the standpoint of naive set theory. No axioms, other than the axiom of choice, are ever stated explicitly, although Zermelo's system is occasionally referred to. But the role of the axiom of choice is a central theme throughout the book. For a student who wishes to learn just when and how this axiom is needed this is the best book yet written. There is an excellent chapter de voted to theorems equivalent to the axiom of choice. These include not only well-ordering, trichotomy, and Zorn's principle, but also several less familiar propositions: Lindenbaum's theorem that of any two nonempty sets one is equivalent to a partition of the other; Vaught's theorem that every family of nonempty sets contains a maximal disjoint family; Tarski's theorem that every cardinal has a successor, and other propositions of cardinal arithmetic; Kurepa's theorem that the proposition that every partially ordered set con tains a maximal family of incomparable elements is an equivalent when joined with the ordering principle, i.e., the proposition that every set can be ordered.