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Publisher:

Chapman & Hall/CRC

Publication Date:

2009

Number of Pages:

525

Format:

Hardcover with CDROM

Series:

Textbooks in Mathematics

Price:

99.95

ISBN:

9781420094527

Category:

Textbook

[Reviewed by , on ]

Richard J. Wilders

11/19/2009

The introduction describes this text as one which could be used for either an undergraduate or a graduate course. The text incorporates technology as a means of reducing computation and allowing students to create their own examples. It is written so as to accommodate either *Mathematica* or a freeware program entitled Groups, Algorithms and Programming (GAP). As an example of how this can simplify life for undergraduates, both *Mathematica* and GAP can verify (by brute force) that A_{5} is simple. However, such a brute force analysis doesn’t really help us to see why A_{5} is a simple group.

Based on my experience, undergraduate students will find the effort required to learn *Mathematica* or GAP notation to exceed the reward of creating the examples. The MAA software package *Exploring Small Groups* is much easier to use. Additionally, *Excel* will create modular arithmetic tables very easily.

The table of contents suggests a traditional order of topics, with group theory being explored in full prior to the introduction of rings. However, the section and chapter headings often don’t match up with what is actually covered. Homework problems are grouped at the end of each chapter. In the chapters I looked closely at, many of the key ideas and examples (e.g., the dihedral groups) appear only in homework problems. This book does not appear to be of sufficient depth or rigor for a graduate text, but the organization of the text makes it inappropriate for undergraduates as well. I outline some of those difficulties below, focusing on four of the chapters.

**Chapter One: Understanding the Group Concept**

As is common, the notion of a group is first introduced through the symmetries of an equilateral triangle. In this case the author introduces Terry the Dancing (equilateral) Triangle. Terry can perform six dance steps each of which corresponds to one of the six members of . Unfortunately, the pictures illustrating Terry’s six moves do not illustrate results of the dance moves as described. Instead, the only pictures provided are taken from “the animation close to the completion of each step.” As a result a rotation of 120 degrees clockwise is illustrated by a figure which appears to have been rotated 60 degrees. The figures illustrating the three reflections show triangles with are no longer equilateral! I think the reader deserves a set of pictures of Terry after he has completed each step. Without that it is not possible to verify the group table that the author presents.

The result is that what could have been a very clever introduction is confusing. The confusion quickly deepens. After stating each of the group axioms in terms of dance steps (STAY is the name used for the “identity dance step.”) At this point the group axioms have not yet been stated in any other terms, only described as dance steps, but we immediately proceed to the following proposition

**PROPOSITION 1.1**If y is an inverse of x, then x is the only inverse of y.

While the Proposition as stated is true, I’m almost certain it was meant to be stated as: “if x is an inverse of y then x is the only inverse of y.” At least that’s what its “proof” proves!

The next example considered is modular arithmetic. The first example is addition mod 10, but the notation used is a dot. That is a + b (Mod 10) is symbolized by a^{.}b. As a result, we see (on page 7) the equation x^{.}0 = 0^{.}x = x. While true in this context, it is likely to be very confusing to beginning students. Part of the confusion is due to the *Mathematica* syntax which uses MultTable for any Cayley Table for a group, so that any group operation is “multiplication.”

The chapter also contains proofs of several facts from elementary number theory. Several of these proofs use the well-ordering of the positive integers, even though this theorem is never explicitly stated. I think these concepts are better reserved for a “chapter 0” (as Gallian and others do in their texts). The chapter concludes with the formal definition of a group. It does not, in my opinion, have enough examples of groups to give beginning students an idea of the richness of the group concept.

**Chapter Two: The Structure within a Group**

There is way too much information here for an undergraduate course. Among the topics (covered in 20 pages) are: generators, subgroups, cyclic groups, the group of units mod n, and some more number theory. At the undergraduate level, each of these concepts is probably worth a chapter in its own right. Here are examples of how condensed things are:

- The subgroup structure of cyclic groups is explored only in the homework.
- The group of units in
**Z**_{n}is defined in the middle of a paragraph in chapter 1. Some 16 pages later, Euler’s totient function is proved to count the number of generators of**Z**_{n}and an example of the group of units is given. - S
_{3}is defined, but there is no reference to the fact that this is part of a family of groups which will appear again in Chapter 5.

**Chapter 4: Mappings between Groups**

Here again, the material is highly condensed. The motivating example of an isomorphism is between a quotient group of the octahedral group and S_{3}! After defining isomorphism, the author proceeds to an enumeration, with proofs, of all the groups (up to isomorphism) of order 8. D_{4} appears, of course — but the only time we have previously encountered this group is as problem 6 in chapter 1. In fact, there is no discussion of the dihedral groups to this point outside of D_{3} and D_{4}. I can’t imagine a typical undergraduate understanding, much less appreciating what’s going on here. Why do we care how many groups of order 8 there are? The author then proceeds to proofs of the three classic isomorphism theorems. The only examples of these are in the exercises. I think undergraduates need lots more examples of actual isomorphisms before we lay all this theory on them.

**Chapter 9: Introduction to Rings**

The first section in this chapter begins by listing a few sets which admit two binary operations. We then leave ring theory altogether for a brief excursion into Cantor’s set theory! The author defines a countable set and proves that the rational numbers are countable and that the real numbers are not. He then returns to the idea of two binary operations without any explanation as to what the previous few pages were about. The first example of a ring is **Z**_{6}, the second is the quaternions. There is a discussion of zero divisors and the fact that elements which are not zero divisors don’t always have inverses, but the notion of the group of units in **Z**_{n} is not discussed. A great deal of space is devoted to the syntax needed to enter ring definitions into *Mathematica* and GAP — the result is that there are far fewer examples than I would like to see in an initial treatment of the ring concept.

At this point, I think it fair to conclude that this text is not competitive with the many fine undergraduate and graduate texts available. I would not recommend this book as either an undergraduate or a graduate text. It is too condensed for an undergraduate text and doesn’t provide enough depth for a graduate text. In addition, the presentation style is not conducive to student learning.

While the use of *Mathematica* or GAP has great potential, it is not sufficient to overcome the deficiencies I observed in these five chapters. In fact, the numerous explanations of the use of *Mathematica* and GAP obscure the presentation. I think these would be more helpful as an appendix or a separate manual.

Richard Wilders is Marie and Bernice Gantzert Professor in the Liberal Arts and Sciences and Professor of Mathematics at North Central College. His primary areas of interest are the history and philosophy of mathematics and of science. He has been a member of the Illinois Section of the Mathematical Association of America for 30 years and is a recipient of its Distinguished Service Award.

**Understanding the Group Concept**

Introduction to Groups

Modular Arithmetic

Prime Factorizations

The Definition of a Group

**The Structure within a Group**

Generators of Groups

Defining Finite Groups in *Mathematica* and GAP

Subgroups

**Patterns within the Cosets of Groups**

Left and Right Cosets

How to Write a Secret Message

Normal Subgroups

Quotient Groups

**Mappings between Groups**

Isomorphisms

Homomorphisms

The Three Isomorphism Theorems

**Permutation Groups**

Symmetric Groups

Cycles

Cayley’s Theorem

Numbering the Permutations

**Building Larger Groups from Smaller Groups**

The Direct Product

The Fundamental Theorem of Finite Abelian Groups

Automorphisms

Semi-Direct Products

**The Search for Normal Subgroups**

The Center of a Group

The Normalizer and Normal Closure Subgroups

Conjugacy Classes and Simple Groups

The Class Equation and Sylow’s Theorems

**Solvable and Insoluble Groups**

Subnormal Series and the Jordan–Hölder Theorem

Derived Group Series

Polycyclic Groups

Solving the Pyraminx™

**Introduction to Rings**

Groups with an Additional Operation

The Definition of a Ring

Entering Finite Rings into GAP and *Mathematica *

Some Properties of Rings

**The Structure within Rings**

Subrings

Quotient Rings and Ideals

Ring Isomorphisms

Homomorphisms and Kernels

**Integral Domains and Fields**

Polynomial Rings

The Field of Quotients

Complex Numbers

Ordered Commutative Rings

**Unique Factorization**

Factorization of Polynomials

Unique Factorization Domains

Principal Ideal Domains

Euclidean Domains

**Finite Division Rings**

Entering Finite Fields in* Mathematica* or GAP

Properties of Finite Fields

Cyclotomic Polynomials

Finite Skew Fields

**The Theory of Fields**

Vector Spaces

Extension Fields

Splitting Fields

**Galois Theory**

The Galois Group of an Extension Field

The Galois Group of a Polynomial in Q

The Fundamental Theorem of Galois Theory

Solutions of Polynomial Equations Using Radicals

**Bibliography **

**Answers to Odd Problems **

**Index**

*Problems appear at the end of each chapter.*

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