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GTM256.A.Course.in.Commutative Algebra.pdf
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详细说明:交换代数GTM256.A.Course.in.Commutative AlgebraTo Idaleixis and martin
Contents
Introduction
鲁鲁
Part I The Algebra geometry Lexicon
1 Hilbert's nullstellensatz
17
1.1 Maximal ideals
18
1.2 Jacobson rin
1. 3 Coordinate rings
26
E
xercises
2 Noetherian and Artinian R ings
2. 1 The Noether and Artin Property for Rings and Modules
2.2 Noetherian Rings and modules,,,...........,. 38
Exercises
3 The Zariski Topology
43
3.1 Affine varictics
13
3.2 Spectra
46
3.3 Noetherian and Irreducible spaces
48
Exercises
4 A Summary of the lexicon
..55
4.1 True geometry: Affine Varieties.............. 55
4.2 Abstract Geometry: Spectra
56
Exercises
.58
Part II Dimension
5 Krull Dimension and Transcendence Degree
Exercises
70
Contents
6 Localizati
73
E
80
7 The Principal Ideal Theorell
85
7. 1 Nakayama's Lemma and the Principal Ideal Theorem
7.2 The Dimension of fibers
Exercises
番番·,番
8 Integral extensions
103
8.1 Integral Closure
103
8.2 Lying Over, Going Up and going Down
8. 3 Noether normalization
114
Exercises
121
Part I Computational Method
9 Grobner bases
127
9. 1 Buchberger's Algorith
128
9.2 First Application: Elimination Ideals
137
Exercises
,143
10 Fibers and Images of morphisms revisited
147
10.1 The Generic Freeness Lemma
147
10.2 Fiber Dimension and Constructible Sets
.152
10.3 Application: Invariant Theory
154
Exercises
158
11 Hilbcrt Scrics and dimension
11. 1 The hilbert-Serre Theorem
161
11.2 Hilbert polynomials and dimension
167
Exercises
171
Part Iv Local Rings
12 Dimension Theory
12. 1 The Length of a Module
177
12.2 The Associated Graded ring
180
E
18
13 Regular Local Rings
191
13. 1 Basic Properties of Regular Local Rings
191
13.2 The Jacobian Criterion
195
E
203
Contents
14 Rings of Dimension One
207
14.1 Regular Rings and normal rings
207
14.2 Multiplicative Ideal theory
211
14.3 Dedekind domains
216
Exercises
Solutions of exercises
227
References
309
Notation
313
nae
垂··鲁垂鲁
315
Introduction
Colninutative algebra is the theory of coInllutative rings Its historic roots are
in invariant, theory, number theory, and, most importantly, geometry. Con
sequently, it nowadays provides the algebraic basis for the fields of algebraic
number theory and algebraic geometry. Over recent decades, commutative al
gebra has also developed a vigorous new branch, computational commutative
algebra, whose goal is to open up the theory to algorithmic computation. so
rather than being an isolated subject, commutative algebra is at the cross-
roads of several important mathematical disciplines
This book has grown out of various courses in commutative algebra that I
nave taught in Hcidclbcrg and Munich. Its primary objcctivc is to scrvc as a
guide for an introductory graduate course of one or two semesters, or for self-
study. I have striven to craft a text that presents the concepts at, the center
of the field in a coherent, tightly knitted way, with streamlined proofs and a
focus on the core results. Needless to say, for an imperfect writer like me, such
high-flying goals will always remain elusive. To introduce readers to the more
recent algorithmic branch of the subject, one part of the book is devoted to
computational mcthods. The connections with gcomctry arc morc than just
applications of coIlImlutative algebra to allother InatheInatical field. In fact
virtually all concepts and results have natural geometric interpretations that
bring out the"true meaning"of the theory. This is why the first part of the
book is entitled "The Algebra geometry Lexicon, and why I have tried to
keep a focus on the geometric context throughout. Hopefully, this will make
the theory more alive for readers, more meaningful, more visual, and easier
to remember
How To Use the book
The main intention of the book is to provide material for an introductory
graduate course of one or two semesters. The duration of the course clearly
depends on such parameters as speed and teaching hours per week and on
10
Introduction
how much material is covered. In the book, I have indicated three options
for skipping material. For example, one possibility is to omit Chapter 10 and
most of Section 7.2. Another is to skip Chapters 9 through 11 almost entirel
But apart from these options, interdependencies in the text are close enough
to makc it hard to skip matcrial without tearing holes into proofs that comc
later. So the instructor can best lilnlit the amount of Material by choosing
where to stop. A relatively short course would stop after Chapter 8, while
other natural stopping points are after Chapter 1l or 13
The book contains a total of 143 exercises. Some of them deal with ex-
amples that illustrate definitions(such as an example of an Artinian module
that is not Noetherian)or shed some light on the necessity of hypotheses of
theorems(such as an example where the principal ideal theorem fails for a
I1Oll-Noethieriall ring). Others give extensions to the theory(such as a series
of exercises that deal with formal power series rings), and yet others invite
readers to do computations on examples. Thesc cxamples oftcn comc from
geometry and also serve to illustrate the theory (such as examples of desingu
larization of curves). Some exercises depend on others, as is usually indicated
in the hints for the exercise. However, no theorem, lemma, or corollary in
the text depends on results from the exercises. I put a star by some exercises
to indicate that i consider them more difficult. Solutions to all exercises are
provided on a cd that comes with the book. In fact, the CD contains an
clectronic vcrsion of thc cntirc book. with solutions to thc cxcrciscs
Although the ideal way of using the book is to read it from the beginning
to the end (every author desires such readers! ) an extensive subject index
hould facilitate a less linear navigation. In the electronic version of the book
all cross-references are realized as hyperlinks, a feature that will appeal to
readers who like working on the screen
Prerequisites
Readers should have taken undergraduate courses in linear algebra and ab
stract algebra. Everything that is assumed, is contained in Lang's book [33]
but certainly not everything in that book is assumed. Specifically, readers
should have a grasp of the following subjects
definition of a(commutative) ring,
ideals, prime ideals and maximal ideals
zero divisors
quotient rings (also known as factor rings)
subrings and hioinoinorphisins of rings
principal ideal domains
factorial rings(also known as unique factorization domains
polynomial rings in several indeterminates
finite field extensions. and
algebraically closed fields
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