# Noncommutative Algebra

Noncommutative Algebra (Graduate Texts in Mathematics) 1993rd Edition

on March 7, 2004
Format: Hardcover
This is a very nice introduction to the theory of semisimple modules and rings, central simple algebras, and the Brauer group. It starts off with some review of basic concepts such as modules, tensor products, and field extensions – much of which is in the exercises. Indeed, a lot of the material is developed in the exercises so it is very useful to go through them. Most of the exercises aren’t exceedingly difficult either, and hints are provided for the more tricky ones.
Chapter one gets the ball rolling with the theory of simple modules and rings. The Wedderburn structure theorem is proved, as well as the structure theorem for simple artinian rings. These ideas are examined further in chapter two by analysing the Jacobson radical, thereby giving another characterization of semisimple rings. Chapter three goes on to study central simple algebras. Here they prove the famous Wedderburn theorem that every finite division ring is commutative, as well as the famous Frobenius theorem on real division algebras. Chapter four finally gives the definition of the Brauer group with a discussion of group cohomology. It proves that for a Galois extension K/k the second Galois cohomology group H^2(Gal(K/k),K*) is isomorphic to the Brauer group Br(K/k). The naturality of this isomorphism is discussed later on and developed through the exercises, although they never actually define what natuarality really is.
One way I think the book could be improved would be to introduce some more abstract homological algebra. The definition of group cohomology given is in terms of n-cochains. I think it would be useful to include the notion of derived functors here, and the general definition of the cohomolgy homology of a derived functor through the use of injective and projective resolutions. Then the group cohomology could be defined using the Ext functors, and the cocycle complexes obtained by examined the particular projective resolution called the Eilenberg-MacLane bar resolution. This method would help introduce the reader to homological algebra, and at the same time give some concrete use of such abstract constructions. The authors generally shy away from categorical language though, which might appeal to some readers.
The later chapters discuss primitive rings, some representation theory of finite groups, dimension theory of rings, and the Brauer group of a commutative ring. I have not gone through this later material in detail (yet), so I cannot give comment on it.
Overall, if you want to learn some non-commutative algebra, by all means buy this book and work out as many exercises as you can. I found the exposition to be quite illuminating and overall very well written. # A Book in Metric Spaces

Metric Spaces (Springer Undergraduate Mathematics Series) 2007th Edition ### Review

From the reviews:

“This book is truly about metric spaces. … The book is packed full of material which does not often appear in comparable books. … His use of questions to increase understanding and to move on to the next topic are also to be appreciated. … this is a great book and suitable … for third-and fourth-year under-graduates and beginning graduate students.” (Marion Cohen, MathDL, January, 2007)

“The book is very readable. It includes appendixes on the necessary mathematical logic and set theory, and has a substantial number of exercises… Every concept is demonstrated via a large number of examples, starting with commonplace ones and expanding the reader’s horizon with the more abstruse ones, to give a sense of the scope of the concepts… A useful addition to any library supporting an undergraduate mathematics major.” (D. Z. Spicer, CHOICE, March, 2007)

### From the Back Cover

The abstract concepts of metric ces are often perceived as difficult. This book offers a unique approach to the subject which gives readers the advantage of a new perspective familiar from the analysis of a real line. Rather than passing quickly from the definition of a metric to the more abstract concepts of convergence and continuity, the author takes the concrete notion of distance as far as possible, illustrating the text with examples and naturally arising questions. Attention to detail at this stage is designed to prepare the reader to understand the more abstract ideas with relative ease.

The book goes on to provide a thorough exposition of all the standard necessary results of the theory and, in addition, includes selected topics not normally found in introductory books, such as: the Tietze Extension Theorem; the Hausdorff metric and its completeness; and the existence of curves of minimum length. Other features include:

• end-of-chapter summaries and numerous exercises to reinforce what has been learnt;
• a Cumulative Reference Chart, showing the dependencies throughout the book on a section-by-section basis as an aid to course design.

The book is designed for third- and fourth-year undergraduates and beginning graduates. Readers should have some practical knowledge of differential and integral calculus and have completed a first course in real analysis. With its many examples, careful illustrations, and full solutions to selected exercises, this book provides a gentle introduction that is ideal for self-study and an excellent preparation for applications. 