To the Teacher. This book is designed to introduce a student to some of the important ideas of algebraic topology by emphasizing the re­ lations of these ideas with other areas of mathematics. Rather than choosing one point of view of modem topology (homotopy theory, simplicial complexes, singular theory, axiomatic homology, differ­ ential topology, etc.), we concentrate our attention on concrete prob­ lems in low dimensions, introducing only as much algebraic machin­ ery as necessary for the problems we meet. This makes it possible to see a wider variety of important features of the subject than is usual in a beginning text. The book is designed for students of mathematics or science who are not aiming to become practicing algebraic topol­ ogists-without, we hope, discouraging budding topologists. We also feel that this approach is in better harmony with the historical devel­ opment of the subject. What would we like a student to know after a first course in to­ pology (assuming we reject the answer: half of what one would like the student to know after a second course in topology)? Our answers to this have guided the choice of material, which includes: under­ standing the relation between homology and integration, first on plane domains, later on Riemann surfaces and in higher dimensions; wind­ ing numbers and degrees of mappings, fixed-point theorems; appli­ cations such as the Jordan curve theorem, invariance of domain; in­ dices of vector fields and Euler characteristics; fundamental groups

Inhalt

I Calculus in the Plane.- 1 Path Integrals.- 1a. Differential Forms and Path Integrals.- 1b. When Are Path Integrals Independent of Path?.- 1c. A Criterion for Exactness.- 2 Angles and Deformations.- 2a. Angle Functions and Winding Numbers.- 2b. Reparametrizing and Deforming Paths.- 2c. Vector Fields and Fluid Flow.- II Winding Numbers.- 3 The Winding Number.- 3a. Definition of the Winding Number.- 3b. Homotopy and Reparametrization.- 3c. Varying the Point.- 3d. Degrees and Local Degrees.- 4 Applications of Winding Numbers.- 4a. The Fundamental Theorem of Algebra.- 4b. Fixed Points and Retractions.- 4c. Antipodes.- 4d. Sandwiches.- III Cohomology and Homology, I.- 5 De Rham Cohomology and the Jordan Curve Theorem.- 5a. Definitions of the De Rham Groups.- 5b. The Coboundary Map.- 5c. The Jordan Curve Theorem.- 5d. Applications and Variations.- 6 Homology.- 6a. Chains, Cycles, and H0U.- 6b. Boundaries, H1U, and Winding Numbers.- 6c. Chains on Grids.- 6d. Maps and Homology.- 6e. The First Homology Group for General Spaces.- IV Vector Fields.- 7 Indices of Vector Fields.- 7a. Vector Fields in the Plane.- 7b. Changing Coordinates.- 7c. Vector Fields on a Sphere.- 8 Vector Fields on Surfaces.- 8a. Vector Fields on a Torus and Other Surfaces.- 8b. The Euler Characteristic.- V Cohomology and Homology, II.- 9 Holes and Integrals.- 9a. Multiply Connected Regions.- 9b. Integration over Continuous Paths and Chains.- 9c. Periods of Integrals.- 9d. Complex Integration.- 10 Mayer-Vietoris.- 10a. The Boundary Map.- 10b. Mayer-Vietoris for Homology.- 10c. Variations and Applications.- 10d. Mayer-Vietoris for Cohomology.- VI Covering Spaces and Fundamental Groups, I.- 11 Covering Spaces.- 11a. Definitions.- 11b. Lifting Paths and Homotopies.- 11c. G-Coverings.- 11d. Covering Transformations.- 12 The Fundamental Group.- 12a. Definitions and Basic Properties.- 12b. Homotopy.- 12c. Fundamental Group and Homology.- VII Covering Spaces and Fundamental Groups, II.- 13 The Fundamental Group and Covering Spaces.- 13a. Fundamental Group and Coverings.- 13b. Automorphisms of Coverings.- 13c. The Universal Covering.- 13d. Coverings and Subgroups of the Fundamental Group.- 14 The Van Kampen Theorem.- 14a. G-Coverings from the Universal Covering.- 14b. Patching Coverings Together.- 14c. The Van Kampen Theorem.- 14d. Applications: Graphs and Free Groups.- VIII Cohomology and Homology, III.- 15 Cohomology.- 15a. Patching Coverings and ?ech Cohomology.- 15b. ?ech Cohomology and Homology.- 15c. De Rham Cohomology and Homology.- 15d. Proof of Mayer-Vietoris for De Rham Cohomology.- 16 Variations.- 16a. The Orientation Covering.- 16b. Coverings from 1-Forms.- 16c. Another Cohomology Group.- 16d. G-Sets and Coverings.- 16e. Coverings and Group Homomorphisms.- 16f. G-Coverings and Cocycles.- IX Topology of Surfaces.- 17 The Topology of Surfaces.- 17a. Triangulation and Polygons with Sides Identified.- 17b. Classification of Compact Oriented Surfaces.- 17c. The Fundamental Group of a Surface.- 18 Cohomology on Surfaces.- 18a. 1-Forms and Homology.- 18b. Integrals of 2-Forms.- 18c. Wedges and the Intersection Pairing.- 18d. De Rham Theory on Surfaces.- X Riemann Surfaces.- 19 Riemann Surfaces.- 19a. Riemann Surfaces and Analytic Mappings.- 19b. Branched Coverings.- 19c. The Riemann-Hurwitz Formula.- 20 Riemann Surfaces and Algebraic Curves.- 20a. The Riemann Surface of an Algebraic Curve.- 20b. Meromorphic Functions on a Riemann Surface.- 20c. Holomorphic and Meromorphic 1-Forms.- 20d. Riemann's Bilinear Relations and the Jacobian.- 20e. Elliptic and Hyperelliptic Curves.- 21 The Riemann-Roch Theorem.- 21a. Spaces of Functions and 1-Forms.- 21b. Adeles.- 21c. Riemann-Roch.- 21d. The Abel-Jacobi Theorem.- XI Higher Dimensions.- 22 Toward Higher Dimensions.- 22a. Holes and Forms in 3-Space.- 22b. Knots.- 22c. Higher Homotopy Groups.- 22d. Higher De Rham Cohomology.- 22e. Cohomology with Compact Supports.- 23 Higher Homology.- 23a. Homology Groups.- 23b. Mayer-Vietoris for Homology.- 23c. Spheres and Degree.- 23d. Generalized Jordan Curve Theorem.- 24 Duality.- 24a. Two Lemmas from Homological Algebra.- 24b. Homology and De Rham Cohomology.- 24c. Cohomology and Cohomology with Compact Supports.- 24d. Simplicial Complexes.- Appendices.- Appendix A Point Set Topology.- A1. Some Basic Notions in Topology.- A2. Connected Components.- A3. Patching.- A4. Lebesgue Lemma.- Appendix B Analysis.- B1. Results from Plane Calculus.- B2. Partition of Unity.- Appendix C Algebra.- C1. Linear Algebra.- C2. Groups; Free Abelian Groups.- C3. Polynomials; Gauss's Lemma.- Appendix D On Surfaces.- D1. Vector Fields on Plane Domains.- D2. Charts and Vector Fields.- D3. Differential Forms on a Surface.- Appendix E Proof of Borsuk's Theorem.- Hints and Answers.- References.- Index of Symbols.