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A Proof of Cantor's Theorem
Cantor’s Theorem Joe Roussos 1 Preliminary ideas Two sets have the same number of elements (are equinumerous, or have the same cardinality) iff there is a bijection between the two sets. Mappings: A mapping, or function, is a rule that associates elements of one set with elements of another set. We write this f : X ! Y , f is called the function/mapping, the set X is called the domain, and Y is called the codomain. We specify what the rule is by writing f(x) = y or f : x 7! y. e.g. X = f1; 2; 3g;Y = f2; 4; 6g, the map f(x) = 2x associates each element x 2 X with the element in Y that is double it. A bijection is a mapping that is injective and surjective.1 • Injective (one-to-one): A function is injective if it takes each element of the do- main onto at most one element of the codomain. It never maps more than one element in the domain onto the same element in the codomain. Formally, if f is a function between set X and set Y , then f is injective iff 8a; b 2 X; f(a) = f(b) ! a = b • Surjective (onto): A function is surjective if it maps something onto every element of the codomain. It can map more than one thing onto the same element in the codomain, but it needs to hit everything in the codomain. Formally, if f is a function between set X and set Y , then f is surjective iff 8y 2 Y; 9x 2 X; f(x) = y Figure 1: Injective map. -
A Surface of Maximal Canonical Degree 11
A SURFACE OF MAXIMAL CANONICAL DEGREE SAI-KEE YEUNG Abstract. It is known since the 70's from a paper of Beauville that the degree of the rational canonical map of a smooth projective algebraic surface of general type is at most 36. Though it has been conjectured that a surface with optimal canonical degree 36 exists, the highest canonical degree known earlier for a min- imal surface of general type was 16 by Persson. The purpose of this paper is to give an affirmative answer to the conjecture by providing an explicit surface. 1. Introduction 1.1. Let M be a minimal surface of general type. Assume that the space of canonical 0 0 sections H (M; KM ) of M is non-trivial. Let N = dimCH (M; KM ) = pg, where pg is the geometric genus. The canonical map is defined to be in general a rational N−1 map ΦKM : M 99K P . For a surface, this is the most natural rational mapping to study if it is non-trivial. Assume that ΦKM is generically finite with degree d. It is well-known from the work of Beauville [B], that d := deg ΦKM 6 36: We call such degree the canonical degree of the surface, and regard it 0 if the canonical mapping does not exist or is not generically finite. The following open problem is an immediate consequence of the work of [B] and is implicitly hinted there. Problem What is the optimal canonical degree of a minimal surface of general type? Is there a minimal surface of general type with canonical degree 36? Though the problem is natural and well-known, the answer remains elusive since the 70's. -
An Update on the Four-Color Theorem Robin Thomas
thomas.qxp 6/11/98 4:10 PM Page 848 An Update on the Four-Color Theorem Robin Thomas very planar map of connected countries the five-color theorem (Theorem 2 below) and can be colored using four colors in such discovered what became known as Kempe chains, a way that countries with a common and Tait found an equivalent formulation of the boundary segment (not just a point) re- Four-Color Theorem in terms of edge 3-coloring, ceive different colors. It is amazing that stated here as Theorem 3. Esuch a simply stated result resisted proof for one The next major contribution came in 1913 from and a quarter centuries, and even today it is not G. D. Birkhoff, whose work allowed Franklin to yet fully understood. In this article I concentrate prove in 1922 that the four-color conjecture is on recent developments: equivalent formulations, true for maps with at most twenty-five regions. The a new proof, and progress on some generalizations. same method was used by other mathematicians to make progress on the four-color problem. Im- Brief History portant here is the work by Heesch, who developed The Four-Color Problem dates back to 1852 when the two main ingredients needed for the ultimate Francis Guthrie, while trying to color the map of proof—“reducibility” and “discharging”. While the the counties of England, noticed that four colors concept of reducibility was studied by other re- sufficed. He asked his brother Frederick if it was searchers as well, the idea of discharging, crucial true that any map can be colored using four col- for the unavoidability part of the proof, is due to ors in such a way that adjacent regions (i.e., those Heesch, and he also conjectured that a suitable de- sharing a common boundary segment, not just a velopment of this method would solve the Four- point) receive different colors. -
Fibonacci, Kronecker and Hilbert NKS 2007
Fibonacci, Kronecker and Hilbert NKS 2007 Klaus Sutner Carnegie Mellon University www.cs.cmu.edu/∼sutner NKS’07 1 Overview • Fibonacci, Kronecker and Hilbert ??? • Logic and Decidability • Additive Cellular Automata • A Knuth Question • Some Questions NKS’07 2 Hilbert NKS’07 3 Entscheidungsproblem The Entscheidungsproblem is solved when one knows a procedure by which one can decide in a finite number of operations whether a given logical expression is generally valid or is satisfiable. The solution of the Entscheidungsproblem is of fundamental importance for the theory of all fields, the theorems of which are at all capable of logical development from finitely many axioms. D. Hilbert, W. Ackermann Grundzuge¨ der theoretischen Logik, 1928 NKS’07 4 Model Checking The Entscheidungsproblem for the 21. Century. Shift to computer science, even commercial applications. Fix some suitable logic L and collection of structures A. Find efficient algorithms to determine A |= ϕ for any structure A ∈ A and sentence ϕ in L. Variants: fix ϕ, fix A. NKS’07 5 CA as Structures Discrete dynamical systems, minimalist description: Aρ = hC, i where C ⊆ ΣZ is the space of configurations of the system and is the “next configuration” relation induced by the local map ρ. Use standard first order logic (either relational or functional) to describe properties of the system. NKS’07 6 Some Formulae ∀ x ∃ y (y x) ∀ x, y, z (x z ∧ y z ⇒ x = y) ∀ x ∃ y, z (y x ∧ z x ∧ ∀ u (u x ⇒ u = y ∨ u = z)) There is no computability requirement for configurations, in x y both x and y may be complicated. -
ON the CONSTRUCTION of NEW TOPOLOGICAL SPACES from EXISTING ONES Consider a Function F
ON THE CONSTRUCTION OF NEW TOPOLOGICAL SPACES FROM EXISTING ONES EMILY RIEHL Abstract. In this note, we introduce a guiding principle to define topologies for a wide variety of spaces built from existing topological spaces. The topolo- gies so-constructed will have a universal property taking one of two forms. If the topology is the coarsest so that a certain condition holds, we will give an elementary characterization of all continuous functions taking values in this new space. Alternatively, if the topology is the finest so that a certain condi- tion holds, we will characterize all continuous functions whose domain is the new space. Consider a function f : X ! Y between a pair of sets. If Y is a topological space, we could define a topology on X by asking that it is the coarsest topology so that f is continuous. (The finest topology making f continuous is the discrete topology.) Explicitly, a subbasis of open sets of X is given by the preimages of open sets of Y . With this definition, a function W ! X, where W is some other space, is continuous if and only if the composite function W ! Y is continuous. On the other hand, if X is assumed to be a topological space, we could define a topology on Y by asking that it is the finest topology so that f is continuous. (The coarsest topology making f continuous is the indiscrete topology.) Explicitly, a subset of Y is open if and only if its preimage in X is open. With this definition, a function Y ! Z, where Z is some other space, is continuous if and only if the composite function X ! Z is continuous. -
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. -
Injection, Surjection, and Linear Maps
Math 108a Professor: Padraic Bartlett Lecture 12: Injection, Surjection and Linear Maps Week 4 UCSB 2013 Today's lecture is centered around the ideas of injection and surjection as they relate to linear maps. While some of you may have seen these terms before in Math 8, many of you indicated in class that a quick refresher talk on the concepts would be valuable. We do this here! 1 Injection and Surjection: Definitions Definition. A function f with domain A and codomain B, formally speaking, is a collec- tion of pairs (a; b), with a 2 A and b 2 B; such that there is exactly one pair (a; b) for every a 2 A. Informally speaking, a function f : A ! B is just a map which takes each element in A to an element in B. Examples. • f : Z ! N given by f(n) = 2jnj + 1 is a function. • g : N ! N given by g(n) = 2jnj + 1 is also a function. It is in fact a different function than f, because it has a different domain! 2 • j : N ! N defined by h(n) = n is yet another function • The function j depicted below by the three arrows is a function, with domain f1; λ, 'g and codomain f24; γ; Zeusg : 1 24 =@ λ ! γ ' Zeus It sends the element 1 to γ, and the elements λ, ' to 24. In other words, h(1) = γ, h(λ) = 24; and h(') = 24. Definition. We call a function f injective if it never hits the same point twice { i.e. -
Equivalents to the Axiom of Choice and Their Uses A
EQUIVALENTS TO THE AXIOM OF CHOICE AND THEIR USES A Thesis Presented to The Faculty of the Department of Mathematics California State University, Los Angeles In Partial Fulfillment of the Requirements for the Degree Master of Science in Mathematics By James Szufu Yang c 2015 James Szufu Yang ALL RIGHTS RESERVED ii The thesis of James Szufu Yang is approved. Mike Krebs, Ph.D. Kristin Webster, Ph.D. Michael Hoffman, Ph.D., Committee Chair Grant Fraser, Ph.D., Department Chair California State University, Los Angeles June 2015 iii ABSTRACT Equivalents to the Axiom of Choice and Their Uses By James Szufu Yang In set theory, the Axiom of Choice (AC) was formulated in 1904 by Ernst Zermelo. It is an addition to the older Zermelo-Fraenkel (ZF) set theory. We call it Zermelo-Fraenkel set theory with the Axiom of Choice and abbreviate it as ZFC. This paper starts with an introduction to the foundations of ZFC set the- ory, which includes the Zermelo-Fraenkel axioms, partially ordered sets (posets), the Cartesian product, the Axiom of Choice, and their related proofs. It then intro- duces several equivalent forms of the Axiom of Choice and proves that they are all equivalent. In the end, equivalents to the Axiom of Choice are used to prove a few fundamental theorems in set theory, linear analysis, and abstract algebra. This paper is concluded by a brief review of the work in it, followed by a few points of interest for further study in mathematics and/or set theory. iv ACKNOWLEDGMENTS Between the two department requirements to complete a master's degree in mathematics − the comprehensive exams and a thesis, I really wanted to experience doing a research and writing a serious academic paper. -
The Four Color Theorem
Western Washington University Western CEDAR WWU Honors Program Senior Projects WWU Graduate and Undergraduate Scholarship Spring 2012 The Four Color Theorem Patrick Turner Western Washington University Follow this and additional works at: https://cedar.wwu.edu/wwu_honors Part of the Computer Sciences Commons, and the Mathematics Commons Recommended Citation Turner, Patrick, "The Four Color Theorem" (2012). WWU Honors Program Senior Projects. 299. https://cedar.wwu.edu/wwu_honors/299 This Project is brought to you for free and open access by the WWU Graduate and Undergraduate Scholarship at Western CEDAR. It has been accepted for inclusion in WWU Honors Program Senior Projects by an authorized administrator of Western CEDAR. For more information, please contact [email protected]. Western WASHINGTON UNIVERSITY ^ Honors Program HONORS THESIS In presenting this Honors paper in partial requirements for a bachelor’s degree at Western Washington University, I agree that the Library shall make its copies freely available for inspection. I further agree that extensive copying of this thesis is allowable only for scholarly purposes. It is understood that anv publication of this thesis for commercial purposes or for financial gain shall not be allowed without mv written permission. Signature Active Minds Changing Lives Senior Project Patrick Turner The Four Color Theorem The history of mathematics is pervaded by problems which can be stated simply, but are difficult and in some cases impossible to prove. The pursuit of solutions to these problems has been an important catalyst in mathematics, aiding the development of many disparate fields. While Fermat’s Last theorem, which states x ” + y ” = has no integer solutions for n > 2 and x, y, 2 ^ is perhaps the most famous of these problems, the Four Color Theorem proved a challenge to some of the greatest mathematical minds from its conception 1852 until its eventual proof in 1976. -
Math 101 B-Packet
Math 101 B-Packet Scott Rome Winter 2012-13 1 Redefining functions This quarter we have defined a function as a rule which assigns exactly one output to each input, and so far we have been happy with this definition. Unfortunately, this way of thinking of a function is insufficient as things become more complicated in mathematics. For a better understanding of a function, we will first need to define it better. Definition 1.1. Let X; Y be any sets. A function f : X ! Y is a rule which assigns every element of X to an element of Y . The sets X and Y are called the domain and codomain of f respectively. x f(x) y Figure 1: This function f : X ! Y maps x 7! f(x). The green circle indicates the range of the function. Notice y is in the codomain, but f does not map to it. Remark 1.2. It is necessary to define the rule, the domain, and the codomain to define a function. Thus far in the class, we have been \sloppy" when working with functions. Remark 1.3. Notice how in the definition, the function is defined by three things: the rule, the domain, and the codomain. That means you can define functions that seem to be the same, but are actually different as we will see. The domain of a function can be thought of as the set of all inputs (that is, everything in the domain will be mapped somewhere by the function). On the other hand, the codomain of a function is the set of all possible outputs, and a function may not necessarily map to every element of the codomain. -
University of Cape Town Department of Mathematics and Applied Mathematics Faculty of Science
The copyright of this thesis vests in the author. No quotation from it or information derived from it is to be published without full acknowledgementTown of the source. The thesis is to be used for private study or non- commercial research purposes only. Cape Published by the University ofof Cape Town (UCT) in terms of the non-exclusive license granted to UCT by the author. University University of Cape Town Department of Mathematics and Applied Mathematics Faculty of Science Convexity in quasi-metricTown spaces Cape ofby Olivier Olela Otafudu May 2012 University A thesis presented for the degree of Doctor of Philosophy prepared under the supervision of Professor Hans-Peter Albert KÄunzi. Abstract Over the last ¯fty years much progress has been made in the investigation of the hyperconvex hull of a metric space. In particular, Dress, Espinola, Isbell, Jawhari, Khamsi, Kirk, Misane, Pouzet published several articles concerning hyperconvex metric spaces. The principal aim of this thesis is to investigateTown the existence of an injective hull in the categories of T0-quasi-metric spaces and of T0-ultra-quasi- metric spaces with nonexpansive maps. Here several results obtained by others for the hyperconvex hull of a metric space haveCape been generalized by us in the case of quasi-metric spaces. In particular we haveof obtained some original results for the q-hyperconvex hull of a T0-quasi-metric space; for instance the q-hyperconvex hull of any totally bounded T0-quasi-metric space is joincompact. Also a construction of the ultra-quasi-metrically injective (= u-injective) hull of a T0-ultra-quasi- metric space is provided. -
Lambda Calculus and Computation 6.037 – Structure and Interpretation of Computer Programs
Lambda Calculus and Computation 6.037 { Structure and Interpretation of Computer Programs Benjamin Barenblat [email protected] Massachusetts Institute of Technology With material from Mike Phillips, Nelson Elhage, and Chelsea Voss January 30, 2019 Benjamin Barenblat 6.037 Lambda Calculus and Computation : Build a calculating machine that gives a yes/no answer to all mathematical questions. Figure: Alonzo Church Figure: Alan Turing (1912-1954), (1903-1995), lambda calculus Turing machines Theorem (Church, Turing, 1936): These models of computation can't solve every problem. Proof: next! Limits to Computation David Hilbert's Entscheidungsproblem (1928) Benjamin Barenblat 6.037 Lambda Calculus and Computation Figure: Alonzo Church Figure: Alan Turing (1912-1954), (1903-1995), lambda calculus Turing machines Theorem (Church, Turing, 1936): These models of computation can't solve every problem. Proof: next! Limits to Computation David Hilbert's Entscheidungsproblem (1928): Build a calculating machine that gives a yes/no answer to all mathematical questions. Benjamin Barenblat 6.037 Lambda Calculus and Computation Theorem (Church, Turing, 1936): These models of computation can't solve every problem. Proof: next! Limits to Computation David Hilbert's Entscheidungsproblem (1928): Build a calculating machine that gives a yes/no answer to all mathematical questions. Figure: Alonzo Church Figure: Alan Turing (1912-1954), (1903-1995), lambda calculus Turing machines Benjamin Barenblat 6.037 Lambda Calculus and Computation Proof: next! Limits to Computation David Hilbert's Entscheidungsproblem (1928): Build a calculating machine that gives a yes/no answer to all mathematical questions. Figure: Alonzo Church Figure: Alan Turing (1912-1954), (1903-1995), lambda calculus Turing machines Theorem (Church, Turing, 1936): These models of computation can't solve every problem.