Topology
A Categorical Approach
by Bradley, Bryson, Terilla
ISBN: 9780262365024 | Copyright 2020
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A graduate-level textbook that presents basic topology from the perspective of category theory.
This graduate-level textbook on topology takes a unique approach: it reintroduces basic, point-set topology from a more modern, categorical perspective. Many graduate students are familiar with the ideas of point-set topology and they are ready to learn something new about them. Teaching the subject using category theory—a contemporary branch of mathematics that provides a way to represent abstract concepts—both deepens students' understanding of elementary topology and lays a solid foundation for future work in advanced topics.
After presenting the basics of both category theory and topology, the book covers the universal properties of familiar constructions and three main topological properties—connectedness, Hausdorff, and compactness. It presents a fine-grained approach to convergence of sequences and filters; explores categorical limits and colimits, with examples; looks in detail at adjunctions in topology, particularly in mapping spaces; and examines additional adjunctions, presenting ideas from homotopy theory, the fundamental groupoid, and the Seifert van Kampen theorem. End-of-chapter exercises allow students to apply what they have learned. The book expertly guides students of topology through the important transition from undergraduate student with a solid background in analysis or point-set topology to graduate student preparing to work on contemporary problems in mathematics.
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Contents (pg. v) | |
Preface (pg. ix) | |
0: Preliminaries (pg. 1) | |
0.1 Basic Topology (pg. 1) | |
0.2 Basic Category Theory (pg. 3) | |
0.2.1 Categories (pg. 3) | |
0.2.2 Functors (pg. 9) | |
0.2.3 Natural Transformations and the Yoneda Lemma& (pg. 11) | |
0.3 Basic Set Theory (pg. 14) | |
0.3.1 Functions (pg. 14) | |
0.3.2 The Empty Set and One-Point Set (pg. 15) | |
0.3.3 Products and Coproducts in Set (pg. 15) | |
0.3.4 Products and Coproducts in Any Category (pg. 17) | |
0.3.5 Exponentiation in Set (pg. 17) | |
0.3.6 Partially Ordered Sets (pg. 18) | |
Exercises (pg. 19) | |
1: Examples and Constructions (pg. 21) | |
1.1 Examples and Terminology (pg. 21) | |
1.1.1 Examples of Spaces (pg. 21) | |
1.1.2 Examples of Continuous Functions (pg. 23) | |
1.2 The Subspace Topology (pg. 25) | |
1.2.1 The First Characterization (pg. 25) | |
1.2.2 The Second Characterization (pg. 26) | |
1.3 The Quotient Topology (pg. 28) | |
1.3.1 The First Characterization (pg. 28) | |
1.3.2 The Second Characterization (pg. 29) | |
1.4 The Product Topology (pg. 30) | |
1.4.1 The First Characterization (pg. 30) | |
1.4.2 The Second Characterization (pg. 31) | |
1.5 The Coproduct Topology (pg. 32) | |
1.5.1 The First Characterization (pg. 32) | |
1.5.2 The Second Characterization (pg. 33) | |
1.6 Homotopy and the Homotopy Category (pg. 34) | |
Exercises (pg. 36) | |
2: Connectedness and Compactness (pg. 39) | |
2.1 Connectedness (pg. 39) | |
2.1.1 Definitions, Theorems, and Examples (pg. 39) | |
2.1.2 The Functor π0 (pg. 43) | |
2.1.3 Constructions and Connectedness (pg. 44) | |
2.1.4 Local (Path) Connectedness (pg. 46) | |
2.2 Hausdorff Spaces (pg. 47) | |
2.3 Compactness (pg. 48) | |
2.3.1 Definitions, Theorems, and Examples (pg. 48) | |
2.3.2 Constructions and Compactness (pg. 50) | |
2.3.3 Local Compactness (pg. 51) | |
Exercises (pg. 53) | |
3: Limits of Sequences and Filters (pg. 55) | |
3.1 Closure and Interior (pg. 55) | |
3.2 Sequences (pg. 56) | |
3.3 Filters and Convergence (pg. 60) | |
3.4 Tychonoff’s Theorem (pg. 64) | |
3.4.1 Ultrafilters and Compactness (pg. 64) | |
3.4.2 A Proof of Tychonoff’s Theorem (pg. 68) | |
3.4.3 A Little Set Theory (pg. 69) | |
Exercises (pg. 71) | |
4 Categorical Limits and Colimits (pg. 75) | |
4.1 Diagrams Are Functors (pg. 75) | |
4.2 Limits and Colimits (pg. 77) | |
4.3 Examples (pg. 79) | |
4.3.1 Terminal and Initial Objects (pg. 79) | |
4.3.2 Products and Coproducts (pg. 80) | |
4.3.3 Pullbacks and Pushouts (pg. 81) | |
4.3.4 Inverse and Direct Limits (pg. 83) | |
4.3.5 Equalizers and Coequalizers (pg. 85) | |
4.4 Completeness and Cocompleteness (pg. 86) | |
Exercises (pg. 88) | |
5: Adjunctions and the Compact-Open Topology (pg. 91) | |
5.1 Adjunctions (pg. 92) | |
5.1.1 The Unit and Counit of an Adjunction (pg. 93) | |
5.2 Free Forgetful Adjunction in Algebra (pg. 94) | |
5.3 The Forgetful Functor U: Top → Set and Its Adjoints (pg. 96) | |
5.4 Adjoint Functor Theorems (pg. 97) | |
5.5 Compactifications (pg. 98) | |
5.5.1 The OnePoint Compactification (pg. 98) | |
5.5.2 The Stone-Čech Compactification (pg. 99) | |
5.6 The Exponential Topology (pg. 101) | |
5.6.1 The CompactOpen Topology (pg. 104) | |
5.6.2 The Theorems of Ascoli and Arzela (pg. 108) | |
5.6.3 Enrich the Product-Hom Adjunction in Top (pg. 109) | |
5.7 Compactly Generated Weakly Hausdorff Spaces (pg. 110) | |
Exercises (pg. 114) | |
6: Paths, Loops, Cylinders, Suspensions, ... (pg. 115) | |
6.1 Cylinder-Free Path Adjunction (pg. 116) | |
6.2 The Fundamental Groupoid and Fundamental Group& (pg. 118) | |
6.3 The Categories of Pairs and Pointed Spaces& (pg. 121) | |
6.4 The Smash-Hom Adjunction (pg. 122) | |
6.5 The Suspension-Loop Adjunction (pg. 124) | |
6.6 Fibrations and Based Path Spaces (pg. 127) | |
6.6.1 Mapping Path Space and Mapping Cylinder (pg. 129) | |
6.6.2 Examples and Results (pg. 131) | |
6.6.3 Applications of π1S 1 (pg. 137) | |
6.7 The Seifert van Kampen Theorem (pg. 139) | |
6.7.1 Examples (pg. 141) | |
Exercises (pg. 145) | |
Glossary of Symbols (pg. 147) | |
Bibliography (pg. 149) | |
Index (pg. 153) |
Tai-Danae Bradley
Tyler Bryson
John Terilla
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