Thesis (M.Sc.) - Carleton University, 2006. / Includes bibliographical references (p. 70-71). Also available in electronic format on the Internet.

This thesis concerns two-point sets, which are subsets of the real plane which intersect every line in exactly two points. The existence of two-point sets was first shown in 1914 by Mazukiewicz, and since this time, the properties of these objects have been of great intrigue to mathematicians working in both topology and set theory. Arguably, the most famous problem about two-point sets is concerned with their so-called "descriptive complexity"; it remains open, and it appears to be deep. An informal interpretation of the problem, which traces back at least to Erdos, is: The term "two-point" set can be defined in a way that it is easily understood by someone with only a limited amount of mathemat- ical training. Even so, how hard is it to construct a two-point set? Can one give an effective algorithm which describes precisely how to do so? More formally, Erdos wanted to know if there exists a two-point set which is a Borel subset of the plane. An essential tool in showing the existence of a two-point set is the Axiom of Choice, an axiom which is taken to be one of the basic truths of mathematics.

In this paper several equivalences of the axiom of choice are examined. In particular, the axiom of choice, Zorn's lemma, Tukey's lemma, the Hausdorff maximal principle, and the well-ordering theorem are shown to be equivalent. Cardinal and ordinal number theory is also studied. The Schroder-Bernstein theorem is proven and used in establishing order results for cardinal numbers. It is also demonstrated that the first uncountable ordinal space is unique up to order isomorphism. We conclude by encountering several applications of the axiom of choice. In particular, we show that every vector space must have a Hamel basis and that any two Hamel bases for the same space must have the same cardinality. We establish that the Tychonoff product theorem implies the axiom of choice and see the use of the axiom of choice in the proof of the Hahn- Banach theorem.

We will discuss the 9th axiom of Zermelo-Fraenkel set theory with choice, which is often abbreviated ZFC, since it includes the axiom of choice (AC). AC is a controversial axiom that is mathematically equivalent to many well known theorems and has an interesting history in set theory. This thesis is a combination of discussion of the history of the axiom and the reasoning behind why the axiom is controversial. This entails several proofs of theorems that establish the fact that AC is equivalent to such theorems and notions as Tychonoff's Theorem, Zorn's Lemma, the Well-Ordering Theorem, and many more.

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Submitted by Viviane Lima da Cunha (viviane@biblioteca.ufpb.br) on 2015-10-19T12:44:14Z No. of bitstreams: 1 arquivototal.pdf: 685310 bytes, checksum: c2f1ca276071e748c54644c3a47977f8 (MD5) / Approved for entry into archive by Maria Suzana Diniz (msuzanad@hotmail.com) on 2015-10-19T12:44:52Z (GMT) No. of bitstreams: 1 arquivototal.pdf: 685310 bytes, checksum: c2f1ca276071e748c54644c3a47977f8 (MD5) / Made available in DSpace on 2015-10-19T12:44:52Z (GMT). No. of bitstreams: 1 arquivototal.pdf: 685310 bytes, checksum: c2f1ca276071e748c54644c3a47977f8 (MD5) Previous issue date: 2014-08-27 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior - CAPES / The main objective of this work is showing the importance of systems axiomatic in mathematics. We will study some classic axioms, their equivalence and we will see some applications of them. / Este trabalho tem como objetivo fazer uma abordagem sobre a importância de sistemas axiomáticos na Matemática. Estudaremos alguns axiomas clássicos, suas equivalências e veremos algumas aplicações dos mesmos.

On travaille dans ZF, théorie des ensembles sans Axiome du Choix. En considérant des formes plus faibles de l'Axiome du choix, comme l'axiome de Hahn-Banach HB : "Toute forme linéaire sur un sous-espace vectoriel d'un espace vectoriel E, majorée par une forme sous-linéaire p se prolonge en une forme linéaire sur E majorée par p'', ou encore l'axiome de Tychonov T2 : "Un produit de compacts séparés est compact'', on étudie l'existence d'états dans les groupes ordonnés avec unité d'ordre. On poursuit l'étude en établissant des liens entre idéaux à gauche et états sur les C*-algèbres. / We work in ZF, set theory without Axiom of Choice. Using weak forms of Axiom of Choice, for example Hahn-Banach axiom HB : "Every linear form on a vector subspaceof a vector space E, increased by a sublinear form p can be extended to a linear form on E increased by p", or Tychonov axiom T2 : "Every product of compact Haussdorf is compact, we study the existence of states on ordered groups with order unit. We continue giving links between left ideals and states on C*-algebras.

A teoria de conjuntos por vezes deixada de lado em algumas escolas de ensino mÃdio, constitui-se em um elemento primordial para o entendimento das funÃÃes, em especial. A nÃo abordagem, ou a sua abordagem superficial, deixa no estudante uma lacuna difÃcil de ser suprida em estudos posteriores. AliÃs, a lacuna deixada pode dificultar o desempenho do estudante no ensino superior. Diante desta constataÃÃo, à objetivo principal desta dissertaÃÃo fazer uma leitura dos principais tÃpicos ligados à Teoria de Conjuntos do ensino mÃdio, ao mesmo tempo em que faz uma ponte entre estes e outros pontos nÃo menos importantes, tratando conjuntos em uma linguagem mais acadÃmica. SerÃo abordados desde as propriedades e teoremas relacionados a conjuntos finitos, atà a sua generalizaÃÃo para conjuntos infinitos, culminando com o teorema de Cantor-Schroeder-Bernstein, o Axioma da Escolha, e o Lema de Zorn. Para tantos, realizaram-se pesquisas bibliogrÃficas em fontes variadas. / The set theory sometimes left out in some high schools, is in a key element for understanding the functions in particular. Failure to address this issue or its superficial approach leaves the student a difficult gap to be filled in later studies. Incidentally, the left gap may hinder student performance in higher education. If this is so, is the main objective of this work to a reinterpretation of the main topics linked to the high school set theory, while making a bridge between these and other equally important points dealing with sets in a more academic language. Will be covered from the properties and theorems related to finite sets up its generalization to infinite sets, culminating in the Cantor-Schroeder-Bernstein theorem, the Axiom of Choice and Zornâs Lemma. To this end, there were literature searches in various sources.

We introduce the Partition Principle PP, an axiom introduced by Russell in the context of its similarities and differences with the Axiom of Choice AC. We start by proving some properties of PP, and AC, and show that AC, entails PP. To address the problem of whether the converse holds, we develop the Zermelo-Fraenkel ZF set theory and examine its consistency and build a model in which AC, fails. We follow this with a discussion of forcing, a technique introduced by Paul Cohen to build new models of set theory from existing ones, which have differing properties from the starting model. We conclude by examining candidate models called permutation models where AC, fails, which may be useful as candidate models for forcing a model in which PP, holds but AC, does not. We conjecture that such a model exists, and that PP, does not entail AC. / Thesis / Master of Science (MSc)

In dieser Arbeit möchte ich dem Wesen des Auswahlaxioms auf den Grund gehen und verstehen, inwieweit es problematisch sein könnte, es zu benutzen, aber auch wie nützlich es ist, dieses mächtige Instrument als Mathematiker zu besitzen.