RUBIK's CUBE from a GROUP-THEORETICAL VIEWPOINT 1. Introduction Ern˝O Rubik's “Magic Cube” Has, Since Its Invention In
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THE UPPER BOUND of COMPOSITION SERIES 1. Introduction. a Composition Series, That Is a Series of Subgroups Each Normal in the Pr
THE UPPER BOUND OF COMPOSITION SERIES ABHIJIT BHATTACHARJEE Abstract. In this paper we prove that among all finite groups of or- α1 α2 αr der n2 N with n ≥ 2 where n = p1 p2 :::pr , the abelian group with elementary abelian sylow subgroups, has the highest number of composi- j Pr α ! Qr Qαi pi −1 ( i=1 i) tion series and it has i=1 j=1 Qr distinct composition pi−1 i=1 αi! series. We also prove that among all finite groups of order ≤ n, n 2 N α with n ≥ 4, the elementary abelian group of order 2 where α = [log2 n] has the highest number of composition series. 1. Introduction. A composition series, that is a series of subgroups each normal in the previous such that corresponding factor groups are simple. Any finite group has a composition series. The famous Jordan-Holder theo- rem proves that, the composition factors in a composition series are unique up to isomorphism. Sometimes a group of small order has a huge number of distinct composition series. For example an elementary abelian group of order 64 has 615195 distinct composition series. In [6] there is an algo- rithm in GAP to find the distinct composition series of any group of finite order.The aim of this paper is to provide an upper bound of the number of distinct composition series of any group of finite order. The approach of this is combinatorial and the method is elementary. All the groups considered in this paper are of finite order. 2. Some Basic Results On Composition Series. -
Topics in Module Theory
Chapter 7 Topics in Module Theory This chapter will be concerned with collecting a number of results and construc- tions concerning modules over (primarily) noncommutative rings that will be needed to study group representation theory in Chapter 8. 7.1 Simple and Semisimple Rings and Modules In this section we investigate the question of decomposing modules into \simpler" modules. (1.1) De¯nition. If R is a ring (not necessarily commutative) and M 6= h0i is a nonzero R-module, then we say that M is a simple or irreducible R- module if h0i and M are the only submodules of M. (1.2) Proposition. If an R-module M is simple, then it is cyclic. Proof. Let x be a nonzero element of M and let N = hxi be the cyclic submodule generated by x. Since M is simple and N 6= h0i, it follows that M = N. ut (1.3) Proposition. If R is a ring, then a cyclic R-module M = hmi is simple if and only if Ann(m) is a maximal left ideal. Proof. By Proposition 3.2.15, M =» R= Ann(m), so the correspondence the- orem (Theorem 3.2.7) shows that M has no submodules other than M and h0i if and only if R has no submodules (i.e., left ideals) containing Ann(m) other than R and Ann(m). But this is precisely the condition for Ann(m) to be a maximal left ideal. ut (1.4) Examples. (1) An abelian group A is a simple Z-module if and only if A is a cyclic group of prime order. -
Composition Series of Arbitrary Cardinality in Abelian Categories
COMPOSITION SERIES OF ARBITRARY CARDINALITY IN ABELIAN CATEGORIES ERIC J. HANSON AND JOB D. ROCK Abstract. We extend the notion of a composition series in an abelian category to allow the mul- tiset of composition factors to have arbitrary cardinality. We then provide sufficient axioms for the existence of such composition series and the validity of “Jordan–Hölder–Schreier-like” theorems. We give several examples of objects which satisfy these axioms, including pointwise finite-dimensional persistence modules, Prüfer modules, and presheaves. Finally, we show that if an abelian category with a simple object has both arbitrary coproducts and arbitrary products, then it contains an ob- ject which both fails to satisfy our axioms and admits at least two composition series with distinct cardinalities. Contents 1. Introduction 1 2. Background 4 3. Subobject Chains 6 4. (Weakly) Jordan–Hölder–Schreier objects 12 5. Examples and Discussion 21 References 28 1. Introduction The Jordan–Hölder Theorem (sometimes called the Jordan–Hölder–Schreier Theorem) remains one of the foundational results in the theory of modules. More generally, abelian length categories (in which the Jordan–Hölder Theorem holds for every object) date back to Gabriel [G73] and remain an important object of study to this day. See e.g. [K14, KV18, LL21]. The importance of the Jordan–Hölder Theorem in the study of groups, modules, and abelian categories has also motivated a large volume work devoted to establishing when a “Jordan–Hölder- like theorem” will hold in different contexts. Some recent examples include exact categories [BHT21, E19+] and semimodular lattices [Ro19, P19+]. In both of these examples, the “composition series” arXiv:2106.01868v1 [math.CT] 3 Jun 2021 in question are assumed to be of finite length, as is the case for the classical Jordan-Hölder Theorem. -
A Splitting Theorem for Linear Polycyclic Groups
New York Journal of Mathematics New York J. Math. 15 (2009) 211–217. A splitting theorem for linear polycyclic groups Herbert Abels and Roger C. Alperin Abstract. We prove that an arbitrary polycyclic by finite subgroup of GL(n, Q) is up to conjugation virtually contained in a direct product of a triangular arithmetic group and a finitely generated diagonal group. Contents 1. Introduction 211 2. Restatement and proof 212 References 216 1. Introduction A linear algebraic group defined over a number field K is a subgroup G of GL(n, C),n ∈ N, which is also an affine algebraic set defined by polyno- mials with coefficients in K in the natural coordinates of GL(n, C). For a subring R of C put G(R)=GL(n, R) ∩ G.LetB(n, C)andT (n, C)bethe (Q-defined linear algebraic) subgroups of GL(n, C) of upper triangular or diagonal matrices in GL(n, C) respectively. Recall that a group Γ is called polycyclic if it has a composition series with cyclic factors. Let Q be the field of algebraic numbers in C.Every discrete solvable subgroup of GL(n, C) is polycyclic (see, e.g., [R]). 1.1. Let o denote the ring of integers in the number field K.IfH is a solvable K-defined algebraic group then H(o) is polycyclic (see [S]). Hence every subgroup of a group H(o)×Δ is polycyclic, if Δ is a finitely generated abelian group. Received November 15, 2007. Mathematics Subject Classification. 20H20, 20G20. Key words and phrases. Polycyclic group, arithmetic group, linear group. -
Megaminx 1/26/12 3:24 PM
Megaminx 1/26/12 3:24 PM Megaminx http://www.jaapsch.net/puzzles/megaminx.htm Page 1 of 5 Megaminx 1/26/12 3:24 PM This is a variant of the Rubik's cube, in the shape of a dodecahedron. It is a very logical progression from the cube to the dodecahedron, as can be seen from the fact that the mechanism is virtually the same, and that many people invented it simultaneously. To quote from Cubic Circular, Issue 3&4, (David Singmaster, Spring&Summer 1982): "The Magic Dodecahedron has been contemplated for some time. So far I have seen photos or models from: Ben Halpern (USA), Boris Horvat (Yugoslavia), Barry Lockwood (UK) and Miklós Kristóf (Hungary), while Kersten Meier (Germany) sent plans in early 1981. I have heard that Christoph Bandelow and Doctor Moll (Germany) have patents and that Mario Ouellette and Luc Robillard (Canada) have both found mechanisms. The Hungarian version is notable as being in production ... and as having planes closer to the centre so each face has a star pattern." "Uwe Mèffert has bought the Halpern and Meier rights, which were both filed on the same day about a month before Kristóf. However there is an unresolved dispute over the extent of overlap in designs." There are several versions that have been made. The standard megaminx has either 6 colours or 12 colours. The face layers are fairly thin, so the edge pieces have some width to them. A version called the Supernova was made in Hungary, and it has 12 colours and thicker face layers which meet exactly at the middle of an edge. -
Classifying Categories the Jordan-Hölder and Krull-Schmidt-Remak Theorems for Abelian Categories
U.U.D.M. Project Report 2018:5 Classifying Categories The Jordan-Hölder and Krull-Schmidt-Remak Theorems for Abelian Categories Daniel Ahlsén Examensarbete i matematik, 30 hp Handledare: Volodymyr Mazorchuk Examinator: Denis Gaidashev Juni 2018 Department of Mathematics Uppsala University Classifying Categories The Jordan-Holder¨ and Krull-Schmidt-Remak theorems for abelian categories Daniel Ahlsen´ Uppsala University June 2018 Abstract The Jordan-Holder¨ and Krull-Schmidt-Remak theorems classify finite groups, either as direct sums of indecomposables or by composition series. This thesis defines abelian categories and extends the aforementioned theorems to this context. 1 Contents 1 Introduction3 2 Preliminaries5 2.1 Basic Category Theory . .5 2.2 Subobjects and Quotients . .9 3 Abelian Categories 13 3.1 Additive Categories . 13 3.2 Abelian Categories . 20 4 Structure Theory of Abelian Categories 32 4.1 Exact Sequences . 32 4.2 The Subobject Lattice . 41 5 Classification Theorems 54 5.1 The Jordan-Holder¨ Theorem . 54 5.2 The Krull-Schmidt-Remak Theorem . 60 2 1 Introduction Category theory was developed by Eilenberg and Mac Lane in the 1942-1945, as a part of their research into algebraic topology. One of their aims was to give an axiomatic account of relationships between collections of mathematical structures. This led to the definition of categories, functors and natural transformations, the concepts that unify all category theory, Categories soon found use in module theory, group theory and many other disciplines. Nowadays, categories are used in most of mathematics, and has even been proposed as an alternative to axiomatic set theory as a foundation of mathematics.[Law66] Due to their general nature, little can be said of an arbitrary category. -
How to Solve the Rubik's Cube 03/11/2007 05:07 PM
How to Solve the Rubik's Cube 03/11/2007 05:07 PM Rubik's Revolution Rubik's Cubes & Puzzles Rubik Cube Boston's Wig Store Everything you wanted to know Rubiks Cube 4x4, Keychain & Huge selection of Rubik Cube Great selection & service Serving about the all new electronic Twist In Stock Now-Free Shipping items. the Boston area Rubik’s cube Over $75 eBay.com www.mayswigs.com www.rubiksrevolution.com AwesomeAvenue.biz Ads by Goooooogle Advertise on this site How to Solve the Rubik's Cube This page is featured under Recreation:Games:Puzzles:Rubik's Cube:Solutions in Yahoo! My Home Page | My Blog | My NHL Shootout Stats 2006-2007 There are three translations of this page: Danish (Dansk) (Word Document), Japanese (日本語) (HTML) and Portuguese (Português) (HTML). If you want to translate this page, go ahead. Send me an email when you are done and I will add your translation to this list. So you have a Rubik's Cube, and you've played with it and stared at it and taken it apart...need I go on any further? The following are two complete, fool-proof solutions to solving the cube from absolutely any legal position. Credit goes not to me, but to David Singmaster, who wrote a book in 1980, Notes on Rubik's Magic Cube, which explains pretty much all of what you need to know, plus more. Singmaster wrote about all of these moves except the move for Step 2, which I discovered independently (along with many other people, no doubt). I've updated this page to include a second solution to the cube. -
Group Theory
Chapter 1 Group Theory Most lectures on group theory actually start with the definition of what is a group. It may be worth though spending a few lines to mention how mathe- maticians came up with such a concept. Around 1770, Lagrange initiated the study of permutations in connection with the study of the solution of equations. He was interested in understanding solutions of polynomials in several variables, and got this idea to study the be- haviour of polynomials when their roots are permuted. This led to what we now call Lagrange’s Theorem, though it was stated as [5] If a function f(x1,...,xn) of n variables is acted on by all n! possible permutations of the variables and these permuted functions take on only r values, then r is a divisior of n!. It is Galois (1811-1832) who is considered by many as the founder of group theory. He was the first to use the term “group” in a technical sense, though to him it meant a collection of permutations closed under multiplication. Galois theory will be discussed much later in these notes. Galois was also motivated by the solvability of polynomial equations of degree n. From 1815 to 1844, Cauchy started to look at permutations as an autonomous subject, and introduced the concept of permutations generated by certain elements, as well as several nota- tions still used today, such as the cyclic notation for permutations, the product of permutations, or the identity permutation. He proved what we call today Cauchy’s Theorem, namely that if p is prime divisor of the cardinality of the group, then there exists a subgroup of cardinality p. -
Composition Series and the Hölder Program
Composition Series and the Holder¨ Program Kevin James Kevin James Composition Series and the H¨olderProgram Remark The fourth isomorphism theorem illustrates how an understanding of the normal subgroups of a given group can help us to understand the group itself better. The proof of the proposition below which is a special case of Cauchy's theorem illustrates how such information can be used inductively to prove theorems. Proposition If G is a finite Abelian group and p is a prime dividing jGj, then G contains an element of order p. Kevin James Composition Series and the H¨olderProgram Definition A group G is called simple if jGj > 1 and the only normal subgroups of G are f1G g and G. Note 1 If G is Abelian and simple then G = Zp. 2 There are both infinite and finite non-abelian groups which are simple. The smallest non-Abelian simple group is A5 which has order 60. Kevin James Composition Series and the H¨olderProgram Definition In a group G a sequence of subgroups 1 = N0 ≤ N1 ≤ · · · ≤ Nk−1 ≤ Nk = G is called a composition series for G if Ni E Ni+1 and Ni+1=Ni is simple for 0 ≤ i ≤ k − 1. If the above sequence is a composition series the quotient groups Ni+1=Ni are called composition factors of G. Theorem (Jordan-Holder)¨ Let 1 6= G be a finite group. Then, 1 G has a composition series 2 The (Jordan H¨older)composition factors in any composition series of G are unique up to isomorphism and rearrangement. -
Section VII.35. Series of Groups
VII.35. Series of Groups 1 Section VII.35. Series of Groups Note. In this section we introduce a way to consider a type of factorization of a group into simple factor groups. This idea is similar to factoring a natural number into prime factors. The big result of this section is the Jordan-H¨older Theorem which gives an indication of why it is important to classify finite simple groups (first encountered in Section III.15). Definition 35.1. A subnormal (or subinvariant) series of a group G is a finite sequence H0, H1,...,Hn of subgroups of G such that Hi < Hi+1 and Hi is a normal subgroup of Hi+1 (i.e., Hi / Hi+1) with H0 = {e} and Hn = G. A normal (or invariant) series of group G is a finite sequence H0, H1,...,Hn of normal subgroups of G (i.e., Hi / G) such that Hi < Hi+1, H0 = {e}, and H0 = G. Note. If Hi is normal in G, then gHi = Hig for all g ∈ G and so Hi is normal in Hi+1 ≤ G. So every normal series of G is also a subnormal series of G. Note. If G is an abelian group, then all subgroups of G are normal, so in this case there is no distinction between a subnormal series and a normal series. Example. A normal series of Z is: {0} < 16Z < 8Z < 4Z < Z. VII.35. Series of Groups 2 Example 35.3. The dihedral group on 4 elements D4 has the subnormal series: {ρ0} < {ρ0, µ1} < {ρ0, ρ2, µ1, µ2} <D4. -
Cubic Circular 07/08/2007 03:35 PM
Cubic Circular 07/08/2007 03:35 PM Cubic Circular The Cubic Circular magazine was written and produced by David Singmaster in the early Eighties. The first issue was a small 16 page pink booklet, of about 19.5 × 14cm. Later issues were on yellow paper and slightly larger at 21 × 14.5cm (A5 format). There were only 5 magazines published, of which 3 were double issues: Issue 1: 16 pages Autumn 1981 Issue 2: 16 pages Spring 1982 Issue 3 & 4: 36 pages Spring & Summer 1982 Issue 5 & 6: 28 pages Autumn & Winter 1982 Issue 7 & 8: 48 pages Summer 1985 David Singmaster still has copies of the Cubic Circular available, so I highly recommend acquiring them from him directly, as they are collectible items. David can be contacted via e-mail (zingmast at sbu.ac.uk) or at: David Singmaster 87 Rodenhurst Road London, SW4 8AF United Kingdom David Singmaster has very kindly allowed me to reproduce the magazines on this site. I have tried to keep it as close to the original as possible, so I have kept the images in the same style (even though most pictures have been redrawn) and kept the same page numbering. A sheet with corrections was included with the first issue, pertaining mostly to the article about Ernö Rubik, so I have inserted it at that point. I have occasionally inserted a comment or correction of my own, and to be clearly distinguishable from David's original text my comments are in italics and in square brackets, [like this - J ]. Below are the Tables of Contents. -
Notices of the American Mathematical Society
The following letter has been sent to all Ph. D. granting mathematics departments November 11, 1975 Dear Colleague: The Council of the American Mathematical Society, at its meeting on 19 August 1975, asked me to address a letter to all chairmen of mathematics departments which award the Ph. D. degree, concerning the present employment situation. At present most graduate students working toward a Ph. D. in "pure" mathematics hope for an academic career, and it is likely that the vast majority of these Ph. D. •s will remain dependent on teaching for their long term employment. You certainly know that new Ph. D. 1s in mathematics have difficulties finding their first academic jobs, and that people have difficulties, perhaps even greater difficulties, in getting a second job. The AMS Committee on Employment and Educational Policy estimates, on the basis of careful studies, that for several years to come, the number of new long term posi tions in colleges and universities will be substantially lower than the current production rate of Ph. D.'s in "pure" mathematics. I refer you, for more precise information, to R. D. An derson's "Doctorates and Jobs", Notices AMS, November 1974 and to Wendell Fleming's "Future Job Prospects for Ph. D.'s in the Mathematical Sciences", Notices AMS, December 1975. While long term predictions in such matters are sometimes unreliable (the very opti mistic predictions in the so-called COSRIMS Report of 1968 were also made by competent people on the basis of careful studies) we must face the present difficulties and the difficul ties which we will certainly encounter in the foreseeable future, responsibly.