A Classical Introduction to Modern Number Theory - GBV

Kenneth Ireland Michael Rosen A Classical Introduction to Modern Number Theory Second Edition Springer...

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Kenneth Ireland Michael Rosen

A Classical Introduction to Modern Number Theory Second Edition

Springer

Contents

Preface to the Second Edition Preface

v vii

CHAPTER 1

Unique Factorization §1 Unique Factorization in Z §2 Unique Factorization in k[x] §3 Unique Factorization in a Principal Ideal Domain §4 The Rings Z[i] and Z[w]

1 1 6 8 12

CHAPTER 2

Applications of Unique Factorization §1 Infinitely Many Primes in Z §2 Some Arithmetic Functions §3 2 \lp Diverges §4 The Growth of ir(x)

17 17 18 21 22

CHAPTER 3

Congruence

28

§1 Elementary Observations §2 Congruence in Z §3 The Congruence ax = b(m) §4 The Chinese Remainder Theorem

28 29 31 34

CHAPTER 4

The Structure of U(Z/nZ) §1 Primitive Roots and the Group Structure of C/(Z/nZ) §2 «th Power Residues

39 39 45

CHAPTER 5

Quadratic Reciprocity . §1 Quadratic Residues §2 Law of Quadratic Reciprocity §3 A Proof of the Law of Quadratic Reciprocity

50 50 53 58 XI

Xll

Contents

CHAPTER 6

Quadratic Gauss Sums §1 Algebraic Numbers and Algebraic Integers §2 The Quadratic Character of 2 • §3 Quadratic Gauss Sums §4 The Sign of the Quadratic Gauss Sum

66 66 69 70 73

CHAPTER 7

Finite Fields §1 Basic Properties of Finite Fields §2 The Existence of Finite Fields §3 An Application to Quadratic Residues

79 79 83 85

CHAPTER 8

Gauss and Jacobi Sums §1 Multiplicative Characters §2 Gauss Sums §3 Jacobi Sums §4 The Equation x" + y" = 1 in Fp §5 More on Jacobi Sums §6 Applications §7 A General Theorem

88 88 91 92 97 98 101 102

CHAPTER 9

Cubic and Biquadratic Reciprocity

108

§1 The Ring Z[o>] §2 Residue Class Rings §3 Cubic Residue Character §4 Proof of the Law of Cubic Reciprocity §5 Another Proof of the Law of Cubic Reciprocity §6 The Cubic Character of 2 §7 Biquadratic Reciprocity: Preliminaries §8 The Quartic Residue Symbol §9 The Law of Biquadratic Reciprocity §10 Rational Biquadratic Reciprocity §11 The Constructibility of Regulär Polygons §12 Cubic Gauss Sums and the Problem of Kummer

109 111 112 115 117 118 119 121 123 127 130 131

CHAPTER 10

Equations over Finite Fields §1 Affine Space, Projective Space, and Polynomials §2 Chevalley's Theorem §3 Gauss and Jacobi Sums over Finite Fields

138 138 143 145

Contents

xiii

CHAPTER 11

The Zeta Function §1 The Zeta Function of a Projective Hypersurface §2 Trace and Norm in Finite Fields §3 The Rationality of the Zeta Function Associated to floJcS1 + aixT + • • • + anx™ §4 A Proof of the Hasse-Davenport Relation §5 The Last Entry

151 151 158 161 163 166

CHAPTER 12

Algebraic Number Theory

172

§1 Algebraic Preliminaries §2 Unique Factonzation in Algebraic Number Fields §3 Ramification and Degree

172 174 181

CHAPTER 13

Quadratic and Cyclotomic Fields §1 Quadratic Number Fields §2 Cyclotomic Fields §3 Quadratic Reciprocity Revisited

188 188 193 199

CHAPTER 14

The Stickelberger Relation and the Eisenstein Reciprocity Law

203

§1 The Norm of an Ideal §2 The Power Residue Symbol §3 The Stickelberger Relation §4 The Proof of the Stickelberger Relation §5 The Proof of the Eisenstein Reciprocity Law §6 Three Applications

203 204 207 209 215 220

CHAPTER 15

Bernoulli Numbers §1 Bernoulli Numbers; Definitions and Applications §2 Congruences Involving Bernoulli Numbers §3 Herbrand's Theorem

228 228 234 241

CHAPTER 16

Dirichlet L-functions §1 The Zeta Function §2 A Special Case §3 Dirichlet Characters §4 Dirichlet L-functions §5 The Key Step §6 Evaluating L(s, x) at Negative Integers

249 249 251 253 255 257 261

XIV

Contents

CHAPTER 17

Diophantine Equations §1 Generalities and First Examples §2 The Method of Descent ' §3 Legendre's Theorem §4 Sophie Germain's Theorem §5 Pell's Equation §6 Sums of Two Squares §7 Sums of Four Squares §8 The Fermat Equation: Exponent 3 §9 Cubic Curves with Infinitely Many Rational Points §10 The Equation y2 = x 3 + k §11 The First Case of Fermat's Conjecture for Regulär Exponent §12 Diophantine Equations and Diophantine Approximation

269 269 271 272 275 276 278 280 284 287 288 290 292

CHAPTER 18

Elliptic Curves

297

§1 Generalities §2 Local and Global Zeta Functions of an Elliptic Curve §3 y2 = x3 + D, the Local Case §4 y2 = x3 - Dx, the Local Case §5 Hecke L-functions §6 y2 = x3 - Dx, the Global Case §7 y2 = x3 + D, the Global Case §8 Final Remarks

297 301 304 306 307 310 312 314

CHAPTER 19

The Mordeil-Weil Theorem

319

§1 The Addition Law and Several Identities §2 The Group EHE §3 The Weak Dirichlet Unit Theorem §4 The Weak Mordell-Weil Theorem §5 The Descent Argument

320 323 326 328 330

CHAPTER 20

New Progress in Arithmetic Geometry

339

§1 The Mordell Conjecture §2 Elliptic Curves §3 Modular Curves §4 Heights and the Height Regulator §5 New Results on the Birch-Swinnerton-Dyer Conjecture §6 Applications to Gauss's Class Number Conjecture

340 343 345 348 353 358

Selected Hints for the Exercises

367

Bibliography

375

Index

385