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20. Group Theory and Generalizations

This volume studies groups as algebraic structures encoding symmetry.

This volume studies groups as algebraic structures encoding symmetry. It develops structural, combinatorial, and computational aspects, along with generalizations such as group actions and extensions.

Part I. Foundations of Group Theory

Chapter 1. Groups

1.1 Definitions and examples 1.2 Subgroups 1.3 Cyclic groups 1.4 Permutation groups 1.5 Basic properties

Chapter 2. Homomorphisms

2.1 Group homomorphisms 2.2 Kernels and images 2.3 Isomorphism theorems 2.4 Automorphisms 2.5 Examples

Chapter 3. Cosets and Lagrange’s Theorem

3.1 Cosets 3.2 Index of a subgroup 3.3 Lagrange’s theorem 3.4 Consequences 3.5 Applications

Part II. Structure Theory

Chapter 4. Normal Subgroups and Quotients

4.1 Normal subgroups 4.2 Quotient groups 4.3 Correspondence theorem 4.4 Examples 4.5 Applications

Chapter 5. Direct and Semidirect Products

5.1 Direct products 5.2 Internal vs external constructions 5.3 Semidirect products 5.4 Applications 5.5 Examples

Chapter 6. Group Actions

6.1 Actions on sets 6.2 Orbits and stabilizers 6.3 Orbit–stabilizer theorem 6.4 Applications 6.5 Examples

Part III. Finite Group Theory

Chapter 7. Sylow Theorems

7.1 p-groups 7.2 Sylow subgroups 7.3 Existence and conjugacy 7.4 Applications 7.5 Examples

Chapter 8. Classification Techniques

8.1 Solvable groups 8.2 Nilpotent groups 8.3 Simple groups 8.4 Composition series 8.5 Jordan–Hölder theorem

Chapter 9. Finite Simple Groups (Overview)

9.1 Definition 9.2 Examples 9.3 Classification theorem (overview) 9.4 Applications 9.5 Significance

Part IV. Infinite Groups

Chapter 10. Infinite Group Structures

10.1 Infinite cyclic groups 10.2 Free groups 10.3 Generators and relations 10.4 Presentations 10.5 Examples

Chapter 11. Growth and Geometry

11.1 Growth of groups 11.2 Cayley graphs 11.3 Geometric group theory (overview) 11.4 Hyperbolic groups (overview) 11.5 Applications

Chapter 12. Topological Groups (Overview)

12.1 Groups with topology 12.2 Continuity of operations 12.3 Examples 12.4 Haar measure (overview) 12.5 Applications

Part V. Representation Theory

Chapter 13. Group Representations

13.1 Linear representations 13.2 Modules over group algebras 13.3 Irreducible representations 13.4 Characters 13.5 Examples

Chapter 14. Character Theory

14.1 Character tables 14.2 Orthogonality relations 14.3 Applications 14.4 Induced representations 14.5 Examples

Chapter 15. Representation of Finite Groups

15.1 Maschke’s theorem 15.2 Decomposition 15.3 Applications 15.4 Examples 15.5 Connections

Part VI. Group Extensions and Cohomology

Chapter 16. Group Extensions

16.1 Extension problems 16.2 Split extensions 16.3 Classification 16.4 Applications 16.5 Examples

Chapter 17. Cohomology of Groups

17.1 Definitions 17.2 Low-dimensional cohomology 17.3 Extensions and cohomology 17.4 Applications 17.5 Examples

Chapter 18. Homological Methods

18.1 Resolutions 18.2 Derived functors 18.3 Applications 18.4 Examples 18.5 Connections

Part VII. Generalizations and Applications

Chapter 19. Group-Like Structures

19.1 Semigroups and monoids 19.2 Groupoids 19.3 Loop structures 19.4 Higher algebraic structures 19.5 Examples

Chapter 20. Applications of Group Theory

20.1 Symmetry in physics 20.2 Crystallography 20.3 Coding theory 20.4 Cryptography 20.5 Combinatorics

Chapter 21. Computational Group Theory

21.1 Algorithms for groups 21.2 Permutation group computation 21.3 Complexity issues 21.4 Software systems 21.5 Applications

Part VIII. Research Directions

Chapter 22. Advanced Topics

22.1 Algebraic groups (overview) 22.2 Lie groups connections 22.3 Geometric group theory 22.4 Infinite-dimensional groups 22.5 Emerging areas

Chapter 23. Open Problems

23.1 Classification challenges 23.2 Representation theory gaps 23.3 Algorithmic complexity 23.4 Structural questions 23.5 Future directions

Chapter 24. Historical and Conceptual Notes

24.1 Development of group theory 24.2 Key contributors 24.3 Evolution of ideas 24.4 Cross-disciplinary impact 24.5 Summary

Appendix

A. Common identities and theorems B. Standard group examples C. Proof techniques checklist D. Algorithm templates E. Cross-reference to other MSC branches

This volume develops group theory as the mathematics of symmetry. It connects algebra, geometry, and applications through structure and action.