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In most major universities one of the three or four basic first-year graduate mathematics courses is algebraic topology. This introductory text is suitable for use in a course on the subject or for self-study, featuring broad coverage and a readable exposition, with many examples and exercises.
The four main chapters present the basics: fundamental group and covering spaces, homology and cohomology, higher homotopy groups, and homotopy theory generally. The author emphasizes the geometric aspects of the subject, which helps students gain intuition.
A unique feature is the inclusion of many optional topics not usually part of a first course due to time constraints: Bockstein and transfer homomorphisms, direct and inverse limits, H-spaces and Hopf algebras, the Brown representability theorem, the James reduced product, the Dold-Thom theorem, and Steenrod squares and powers.
PREFACE
This book was written to be a readable introduction to algebraic topology with rather broad coverage of the subject. The viewpoint is quite classical in spirit, and stays well within the confines of pure algebraic topology. In a sense, the book could have been written thirty or forty years ago since virtually everything in it is at least that old.
However, the passage of the intervening years has helped clarify what are the most important results and techniques. For example, CW complexes have proved over time to be the most natural class of spaces for algebraic topology, so they are emphasized here much more than in the books of an earlier generation. This emphasis also illustrates the book’s general slant towards geometric, rather than algebraic, aspects of the subject. The geometry of algebraic topology is so pretty, it would seem a pity to slight it and to miss all the intuition it provides.
At the elementary level, algebraic topology separates naturally into the two broad channels of homology and homotopy. This material is here divided into four chapters, roughly according to increasing sophistication, with homotopy split between Chapters 1 and 4, and homology and its mirror variant cohomology in Chapters 2 and 3. These four chapters do not have to be read in this order, however. One could begin with homology and perhaps continue with cohomology before turning to homotopy. ...
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Allen Hatcher
2002 by Cambridge University Press
CONTENTS
Preface . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ix
Standard Notations xii.
Chapter 0. Some Underlying Geometric Notions . . . . . 1
Homotopy and Homotopy Type 1. Cell Complexes 5.
Operations on Spaces 8. Two Criteria for Homotopy Equivalence 10.
The Homotopy Extension Property 14.
Chapter 1. The Fundamental Group . . . . . . . . . . . . . 21
1.1. Basic Constructions . . . . . . . . . . . . . . . . . . . . . 25
Paths and Homotopy 25. The Fundamental Group of the Circle 29.
Induced Homomorphisms 34.
1.2. Van Kampen’s Theorem . . . . . . . . . . . . . . . . . . . 40
Free Products of Groups 41. The van Kampen Theorem 43.
Applications to Cell Complexes 50.
1.3. Covering Spaces . . . . . . . . . . . . . . . . . . . . . . . . 56
Lifting Properties 60. The Classification of Covering Spaces 63.
Deck Transformations and Group Actions 70.
Additional Topics
1.A. Graphs and Free Groups 83.
1.B. K(G,1) Spaces and Graphs of Groups 87.
Chapter 2. Homology . . . . . . . . . . . . . . . . . . . . . . . 97
2.1. Simplicial and Singular Homology . . . . . . . . . . . . . 102
Ñ Complexes 102. Simplicial Homology 104. Singular Homology 108.
Homotopy Invariance 110. Exact Sequences and Excision 113.
The Equivalence of Simplicial and Singular Homology 128.
2.2. Computations and Applications . . . . . . . . . . . . . . 134
Degree 134. Cellular Homology 137. Mayer-Vietoris Sequences 149.
Homology with Coefficients 153.
2.3. The Formal Viewpoint . . . . . . . . . . . . . . . . . . . . 160
Axioms for Homology 160. Categories and Functors 162.
Additional Topics
2.A. Homology and Fundamental Group 166.
2.B. Classical Applications 169.
2.C. Simplicial Approximation 177.
Chapter 3. Cohomology . . . . . . . . . . . . . . . . . . . . . 185
3.1. Cohomology Groups . . . . . . . . . . . . . . . . . . . . . 190
The Universal Coefficient Theorem 190. Cohomology of Spaces 197.
3.2. Cup Product . . . . . . . . . . . . . . . . . . . . . . . . . . 206
The Cohomology Ring 211. A K¨unneth Formula 218.
Spaces with Polynomial Cohomology 224.
3.3. Poincar´e Duality . . . . . . . . . . . . . . . . . . . . . . . . 230
Orientations and Homology 233. The Duality Theorem 239.
Connection with Cup Product 249. Other Forms of Duality 252.
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