The Algebraic Theory of Semigroups the Algebraic Theory of Semigroups
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Math 5111 (Algebra 1) Lecture #14 of 24 ∼ October 19Th, 2020
Math 5111 (Algebra 1) Lecture #14 of 24 ∼ October 19th, 2020 Group Isomorphism Theorems + Group Actions The Isomorphism Theorems for Groups Group Actions Polynomial Invariants and An This material represents x3.2.3-3.3.2 from the course notes. Quotients and Homomorphisms, I Like with rings, we also have various natural connections between normal subgroups and group homomorphisms. To begin, observe that if ' : G ! H is a group homomorphism, then ker ' is a normal subgroup of G. In fact, I proved this fact earlier when I introduced the kernel, but let me remark again: if g 2 ker ', then for any a 2 G, then '(aga−1) = '(a)'(g)'(a−1) = '(a)'(a−1) = e. Thus, aga−1 2 ker ' as well, and so by our equivalent properties of normality, this means ker ' is a normal subgroup. Thus, we can use homomorphisms to construct new normal subgroups. Quotients and Homomorphisms, II Equally importantly, we can also do the reverse: we can use normal subgroups to construct homomorphisms. The key observation in this direction is that the map ' : G ! G=N associating a group element to its residue class / left coset (i.e., with '(a) = a) is a ring homomorphism. Indeed, the homomorphism property is precisely what we arranged for the left cosets of N to satisfy: '(a · b) = a · b = a · b = '(a) · '(b). Furthermore, the kernel of this map ' is, by definition, the set of elements in G with '(g) = e, which is to say, the set of elements g 2 N. Thus, kernels of homomorphisms and normal subgroups are precisely the same things. -
Exercises and Solutions in Groups Rings and Fields
EXERCISES AND SOLUTIONS IN GROUPS RINGS AND FIELDS Mahmut Kuzucuo˘glu Middle East Technical University [email protected] Ankara, TURKEY April 18, 2012 ii iii TABLE OF CONTENTS CHAPTERS 0. PREFACE . v 1. SETS, INTEGERS, FUNCTIONS . 1 2. GROUPS . 4 3. RINGS . .55 4. FIELDS . 77 5. INDEX . 100 iv v Preface These notes are prepared in 1991 when we gave the abstract al- gebra course. Our intention was to help the students by giving them some exercises and get them familiar with some solutions. Some of the solutions here are very short and in the form of a hint. I would like to thank B¨ulent B¨uy¨ukbozkırlı for his help during the preparation of these notes. I would like to thank also Prof. Ismail_ S¸. G¨ulo˘glufor checking some of the solutions. Of course the remaining errors belongs to me. If you find any errors, I should be grateful to hear from you. Finally I would like to thank Aynur Bora and G¨uldaneG¨um¨u¸sfor their typing the manuscript in LATEX. Mahmut Kuzucuo˘glu I would like to thank our graduate students Tu˘gbaAslan, B¨u¸sra C¸ınar, Fuat Erdem and Irfan_ Kadık¨oyl¨ufor reading the old version and pointing out some misprints. With their encouragement I have made the changes in the shape, namely I put the answers right after the questions. 20, December 2011 vi M. Kuzucuo˘glu 1. SETS, INTEGERS, FUNCTIONS 1.1. If A is a finite set having n elements, prove that A has exactly 2n distinct subsets. -
On Free Quasigroups and Quasigroup Representations Stefanie Grace Wang Iowa State University
Iowa State University Capstones, Theses and Graduate Theses and Dissertations Dissertations 2017 On free quasigroups and quasigroup representations Stefanie Grace Wang Iowa State University Follow this and additional works at: https://lib.dr.iastate.edu/etd Part of the Mathematics Commons Recommended Citation Wang, Stefanie Grace, "On free quasigroups and quasigroup representations" (2017). Graduate Theses and Dissertations. 16298. https://lib.dr.iastate.edu/etd/16298 This Dissertation is brought to you for free and open access by the Iowa State University Capstones, Theses and Dissertations at Iowa State University Digital Repository. It has been accepted for inclusion in Graduate Theses and Dissertations by an authorized administrator of Iowa State University Digital Repository. For more information, please contact [email protected]. On free quasigroups and quasigroup representations by Stefanie Grace Wang A dissertation submitted to the graduate faculty in partial fulfillment of the requirements for the degree of DOCTOR OF PHILOSOPHY Major: Mathematics Program of Study Committee: Jonathan D.H. Smith, Major Professor Jonas Hartwig Justin Peters Yiu Tung Poon Paul Sacks The student author and the program of study committee are solely responsible for the content of this dissertation. The Graduate College will ensure this dissertation is globally accessible and will not permit alterations after a degree is conferred. Iowa State University Ames, Iowa 2017 Copyright c Stefanie Grace Wang, 2017. All rights reserved. ii DEDICATION I would like to dedicate this dissertation to the Integral Liberal Arts Program. The Program changed my life, and I am forever grateful. It is as Aristotle said, \All men by nature desire to know." And Montaigne was certainly correct as well when he said, \There is a plague on Man: his opinion that he knows something." iii TABLE OF CONTENTS LIST OF TABLES . -
Relations in Categories
Relations in Categories Stefan Milius A thesis submitted to the Faculty of Graduate Studies in partial fulfilment of the requirements for the degree of Master of Arts Graduate Program in Mathematics and Statistics York University Toronto, Ontario June 15, 2000 Abstract This thesis investigates relations over a category C relative to an (E; M)-factori- zation system of C. In order to establish the 2-category Rel(C) of relations over C in the first part we discuss sufficient conditions for the associativity of horizontal composition of relations, and we investigate special classes of morphisms in Rel(C). Attention is particularly devoted to the notion of mapping as defined by Lawvere. We give a significantly simplified proof for the main result of Pavlovi´c,namely that C Map(Rel(C)) if and only if E RegEpi(C). This part also contains a proof' that the category Map(Rel(C))⊆ is finitely complete, and we present the results obtained by Kelly, some of them generalized, i. e., without the restrictive assumption that M Mono(C). The next part deals with factorization⊆ systems in Rel(C). The fact that each set-relation has a canonical image factorization is generalized and shown to yield an (E¯; M¯ )-factorization system in Rel(C) in case M Mono(C). The setting without this condition is studied, as well. We propose a⊆ weaker notion of factorization system for a 2-category, where the commutativity in the universal property of an (E; M)-factorization system is replaced by coherent 2-cells. In the last part certain limits and colimits in Rel(C) are investigated. -
Class Semigroups of Prufer Domains
JOURNAL OF ALGEBRA 184, 613]631Ž. 1996 ARTICLE NO. 0279 Class Semigroups of PruferÈ Domains S. Bazzoni* Dipartimento di Matematica Pura e Applicata, Uni¨ersita di Pado¨a, ¨ia Belzoni 7, 35131 Padua, Italy Communicated by Leonard Lipshitz View metadata, citation and similar papers at Receivedcore.ac.uk July 3, 1995 brought to you by CORE provided by Elsevier - Publisher Connector The class semigroup of a commutative integral domain R is the semigroup S Ž.R of the isomorphism classes of the nonzero ideals of R with the operation induced by multiplication. The aim of this paper is to characterize the PruferÈ domains R such that the semigroup S Ž.R is a Clifford semigroup, namely a disjoint union of groups each one associated to an idempotent of the semigroup. We find a connection between this problem and the following local invertibility property: an ideal I of R is invertible if and only if every localization of I at a maximal ideal of Ris invertible. We consider the Ž.a property, introduced in 1967 for PruferÈ domains R, stating that if D12and D are two distinct sets of maximal ideals of R, Ä 4Ä 4 then F RMM <gD1 /FRMM <gD2 . Let C be the class of PruferÈ domains satisfying the separation property Ž.a or with the property that each localization at a maximal ideal if finite-dimensional. We prove that, if R belongs to C, then the local invertibility property holds on R if and only if every nonzero element of R is contained only in a finite number of maximal ideals of R. -
Noncommutative Unique Factorization Domainso
NONCOMMUTATIVE UNIQUE FACTORIZATION DOMAINSO BY P. M. COHN 1. Introduction. By a (commutative) unique factorization domain (UFD) one usually understands an integral domain R (with a unit-element) satisfying the following three conditions (cf. e.g. Zariski-Samuel [16]): Al. Every element of R which is neither zero nor a unit is a product of primes. A2. Any two prime factorizations of a given element have the same number of factors. A3. The primes occurring in any factorization of a are completely deter- mined by a, except for their order and for multiplication by units. If R* denotes the semigroup of nonzero elements of R and U is the group of units, then the classes of associated elements form a semigroup R* / U, and A1-3 are equivalent to B. The semigroup R*jU is free commutative. One may generalize the notion of UFD to noncommutative rings by taking either A-l3 or B as starting point. It is obvious how to do this in case B, although the class of rings obtained is rather narrow and does not even include all the commutative UFD's. This is indicated briefly in §7, where examples are also given of noncommutative rings satisfying the definition. However, our principal aim is to give a definition of a noncommutative UFD which includes the commutative case. Here it is better to start from A1-3; in order to find the precise form which such a definition should take we consider the simplest case, that of noncommutative principal ideal domains. For these rings one obtains a unique factorization theorem simply by reinterpreting the Jordan- Holder theorem for right .R-modules on one generator (cf. -
The Representation Theorem of Persistence Revisited and Generalized
Journal of Applied and Computational Topology https://doi.org/10.1007/s41468-018-0015-3 The representation theorem of persistence revisited and generalized René Corbet1 · Michael Kerber1 Received: 9 November 2017 / Accepted: 15 June 2018 © The Author(s) 2018 Abstract The Representation Theorem by Zomorodian and Carlsson has been the starting point of the study of persistent homology under the lens of representation theory. In this work, we give a more accurate statement of the original theorem and provide a complete and self-contained proof. Furthermore, we generalize the statement from the case of linear sequences of R-modules to R-modules indexed over more general monoids. This generalization subsumes the Representation Theorem of multidimen- sional persistence as a special case. Keywords Computational topology · Persistence modules · Persistent homology · Representation theory Mathematics Subject Classifcation 06F25 · 16D90 · 16W50 · 55U99 · 68W30 1 Introduction Persistent homology, introduced by Edelsbrunner et al. (2002), is a multi-scale extension of classical homology theory. The idea is to track how homological fea- tures appear and disappear in a shape when the scale parameter is increasing. This data can be summarized by a barcode where each bar corresponds to a homology class that appears in the process and represents the range of scales where the class is present. The usefulness of this paradigm in the context of real-world data sets has led to the term topological data analysis; see the surveys (Carlsson 2009; Ghrist 2008; Edelsbrunner and Morozov 2012; Vejdemo-Johansson 2014; Kerber 2016) and textbooks (Edelsbrunner and Harer 2010; Oudot 2015) for various use cases. * René Corbet [email protected] Michael Kerber [email protected] 1 Institute of Geometry, Graz University of Technology, Kopernikusgasse 24, 8010 Graz, Austria Vol.:(0123456789)1 3 R. -
GROUP ACTIONS 1. Introduction the Groups Sn, An, and (For N ≥ 3)
GROUP ACTIONS KEITH CONRAD 1. Introduction The groups Sn, An, and (for n ≥ 3) Dn behave, by their definitions, as permutations on certain sets. The groups Sn and An both permute the set f1; 2; : : : ; ng and Dn can be considered as a group of permutations of a regular n-gon, or even just of its n vertices, since rigid motions of the vertices determine where the rest of the n-gon goes. If we label the vertices of the n-gon in a definite manner by the numbers from 1 to n then we can view Dn as a subgroup of Sn. For instance, the labeling of the square below lets us regard the 90 degree counterclockwise rotation r in D4 as (1234) and the reflection s across the horizontal line bisecting the square as (24). The rest of the elements of D4, as permutations of the vertices, are in the table below the square. 2 3 1 4 1 r r2 r3 s rs r2s r3s (1) (1234) (13)(24) (1432) (24) (12)(34) (13) (14)(23) If we label the vertices in a different way (e.g., swap the labels 1 and 2), we turn the elements of D4 into a different subgroup of S4. More abstractly, if we are given a set X (not necessarily the set of vertices of a square), then the set Sym(X) of all permutations of X is a group under composition, and the subgroup Alt(X) of even permutations of X is a group under composition. If we list the elements of X in a definite order, say as X = fx1; : : : ; xng, then we can think about Sym(X) as Sn and Alt(X) as An, but a listing in a different order leads to different identifications 1 of Sym(X) with Sn and Alt(X) with An. -
Second-Order Algebraic Theories (Extended Abstract)
Second-Order Algebraic Theories (Extended Abstract) Marcelo Fiore and Ola Mahmoud University of Cambridge, Computer Laboratory Abstract. Fiore and Hur [10] recently introduced a conservative exten- sion of universal algebra and equational logic from first to second order. Second-order universal algebra and second-order equational logic respec- tively provide a model theory and a formal deductive system for lan- guages with variable binding and parameterised metavariables. This work completes the foundations of the subject from the viewpoint of categori- cal algebra. Specifically, the paper introduces the notion of second-order algebraic theory and develops its basic theory. Two categorical equiva- lences are established: at the syntactic level, that of second-order equa- tional presentations and second-order algebraic theories; at the semantic level, that of second-order algebras and second-order functorial models. Our development includes a mathematical definition of syntactic trans- lation between second-order equational presentations. This gives the first formalisation of notions such as encodings and transforms in the context of languages with variable binding. 1 Introduction Algebra started with the study of a few sample algebraic structures: groups, rings, lattices, etc. Based on these, Birkhoff [3] laid out the foundations of a general unifying theory, now known as universal algebra. Birkhoff's formalisation of the notion of algebra starts with the introduction of equational presentations. These constitute the syntactic foundations of the subject. Algebras are then the semantics or model theory, and play a crucial role in establishing the logical foundations. Indeed, Birkhoff introduced equational logic as a sound and complete formal deductive system for reasoning about algebraic structure. -
Right Product Quasigroups and Loops
RIGHT PRODUCT QUASIGROUPS AND LOOPS MICHAEL K. KINYON, ALEKSANDAR KRAPEZˇ∗, AND J. D. PHILLIPS Abstract. Right groups are direct products of right zero semigroups and groups and they play a significant role in the semilattice decomposition theory of semigroups. Right groups can be characterized as associative right quasigroups (magmas in which left translations are bijective). If we do not assume associativity we get right quasigroups which are not necessarily representable as direct products of right zero semigroups and quasigroups. To obtain such a representation, we need stronger assumptions which lead us to the notion of right product quasigroup. If the quasigroup component is a (one-sided) loop, then we have a right product (left, right) loop. We find a system of identities which axiomatizes right product quasigroups, and use this to find axiom systems for right product (left, right) loops; in fact, we can obtain each of the latter by adjoining just one appropriate axiom to the right product quasigroup axiom system. We derive other properties of right product quasigroups and loops, and conclude by show- ing that the axioms for right product quasigroups are independent. 1. Introduction In the semigroup literature (e.g., [1]), the most commonly used definition of right group is a semigroup (S; ·) which is right simple (i.e., has no proper right ideals) and left cancellative (i.e., xy = xz =) y = z). The structure of right groups is clarified by the following well-known representation theorem (see [1]): Theorem 1.1. A semigroup (S; ·) is a right group if and only if it is isomorphic to a direct product of a group and a right zero semigroup. -
Right Ideals of a Ring and Sublanguages of Science
RIGHT IDEALS OF A RING AND SUBLANGUAGES OF SCIENCE Javier Arias Navarro Ph.D. In General Linguistics and Spanish Language http://www.javierarias.info/ Abstract Among Zellig Harris’s numerous contributions to linguistics his theory of the sublanguages of science probably ranks among the most underrated. However, not only has this theory led to some exhaustive and meaningful applications in the study of the grammar of immunology language and its changes over time, but it also illustrates the nature of mathematical relations between chunks or subsets of a grammar and the language as a whole. This becomes most clear when dealing with the connection between metalanguage and language, as well as when reflecting on operators. This paper tries to justify the claim that the sublanguages of science stand in a particular algebraic relation to the rest of the language they are embedded in, namely, that of right ideals in a ring. Keywords: Zellig Sabbetai Harris, Information Structure of Language, Sublanguages of Science, Ideal Numbers, Ernst Kummer, Ideals, Richard Dedekind, Ring Theory, Right Ideals, Emmy Noether, Order Theory, Marshall Harvey Stone. §1. Preliminary Word In recent work (Arias 2015)1 a line of research has been outlined in which the basic tenets underpinning the algebraic treatment of language are explored. The claim was there made that the concept of ideal in a ring could account for the structure of so- called sublanguages of science in a very precise way. The present text is based on that work, by exploring in some detail the consequences of such statement. §2. Introduction Zellig Harris (1909-1992) contributions to the field of linguistics were manifold and in many respects of utmost significance. -
The Cardinality of the Center of a Pi Ring
Canad. Math. Bull. Vol. 41 (1), 1998 pp. 81±85 THE CARDINALITY OF THE CENTER OF A PI RING CHARLES LANSKI ABSTRACT. The main result shows that if R is a semiprime ring satisfying a poly- nomial identity, and if Z(R) is the center of R, then card R Ä 2cardZ(R). Examples show that this bound can be achieved, and that the inequality fails to hold for rings which are not semiprime. The purpose of this note is to compare the cardinality of a ring satisfying a polynomial identity (a PI ring) with the cardinality of its center. Before proceeding, we recall the def- inition of a central identity, a notion crucial for us, and a basic result about polynomial f g≥ f g identities. Let C be a commutative ring with 1, F X Cn x1,...,xn the free algebra f g ≥ 2 f gj over C in noncommuting indeterminateso xi ,andsetG f(x1,...,xn) F X some coef®cient of f is a unit in C .IfRis an algebra over C,thenf(x1,...,xn)2Gis a polyno- 2 ≥ mial identity (PI) for RPif for all ri R, f (r1,...,rn) 0. The standard identity of degree sgõ n is Sn(x1,...,xn) ≥ õ(1) xõ(1) ÐÐÐxõ(n) where õ ranges over the symmetric group on n letters. The Amitsur-Levitzki theorem is an important result about Sn and shows that Mk(C) satis®es Sn exactly for n ½ 2k [5; Lemma 2, p. 18 and Theorem, p. 21]. Call f 2 G a central identity for R if f (r1,...,rn) 2Z(R), the center of R,forallri 2R, but f is not a polynomial identity.