Table of Contents
Preface vii
Questions x
1 Logic 1
1.1 Statements 1
1.2 Implications 5
1.3 Conjunction, Disjunction, and Negation 11
1.4 Special Focus on Negation 19
1.5 Variables and Quantifiers 25
1.6 Proofs 30
1.7 Using Tautologies to Analyze Arguments 42
1.8 Russell's Paradox 46
2 Set Theory 51
2.1 Sets and Objects 52
2.2 The Axiom of Specification 56
2.3 The Axiom of Extension 59
2.4 The Axiom of Unions 67
2.5 The Axiom of Powers, Relations, and Functions 73
2.6 The Axiom of Infinity and the Natural Numbers 83
3 Number Systems I: Natural Numbers 89
3.1 Arithmetic With Natural Numbers 89
3.2 Ordering the Natural Numbers 98
3.3 A More Abstract Viewpoint: Binary Operations 103
3.4 Induction 111
3.5 Sums and Products 120
3.6 Divisibility 133
3.7 Equivalence Relations 142
3.8 Arithmetic Modulo m 147
3.9 Public Key Encryption 153
4 Number Systems II: Integers 161
4.1 Arithmetic With Integers 161
4.2 Groups and Rings 167
4.3 Finding the Natural Numbers in the Integers 175
4.4 Ordered Rings 179
4.5 Division in Rings 185
4.6 Countable Sets 195
5 Number Systems III: Fields 201
5.1 Arithmetic With Rational Numbers 201
5.2 Fields 205
5.3 Ordered Fields 211
5.4 A Problem With the Rational Numbers 213
5.5 The Real Numbers 216
5.6 Uncountable Sets 226
5.7 The Complex Numbers 230
5.8 Solving Polynomial Equations 233
5.9 Beyond Fields: Vector Spaces and Algebras 243
6 Unsolvability of the Quintic by Radicals 249
6.1 Irreducible Polynomials 250
6.2 Field Extensions and Splitting Fields 255
6.3 Uniqueness of the Splitting Field 260
6.4 Field Automorphisms and Galois Groups 269
6.5 Normal Field Extensions 273
6.6 The Groups Sn 276
6.7 The Fundamental Theorem of Galois Theory and Normal Subgroups 281
6.8 Consequences of Solvability by Radicals 292
6.9 Abel's Theorem 298
7 More Axioms 301
7.1 The Axiom of Choice, Zorn's Lemma, and the Well-Ordering Theorem 301
7.2 Ordinal Numbers and the Axiom of Replacement 308
7.3 Cardinal Numbers and the Continuum Hypothesis 311
A Historical Overview and Commentary 317
A.1 Ancient Times: Greece and Rome 318
A.2 The Dark Ages and First New Developments 321
A.3 There is No Quintic Formula: Abel and Galois 323
A.4 Understanding Irrational Numbers: Set Theory 326
Conclusion and Outlook 328
Bibliography 329
Index 333