Math 81/111 Abstract Algebra: Field and Galois Theory


Require textbook (referred to as DF):

  • David S. Dummit and Richard M. Foote, Abstract Algebra, 3rd Edition

List of other useful texts and resources:

  • J. S. Milne, Fields and Galois Theory, (referred to as FT) available online via Milne's website
  • J. S. Milne, Algebraic Number Theory, (referred to as ANT) available online via Milne's website
  • Juliusz BrzeziƄski, Galois theory through exercises, available on-line via SpringerLink
  • Keith Conrad's expository notes
  • Serge Lang, Algebra, Graduate Texts in Mathematics, vol. 211, Third edition, 2005.
  • Ian Stewart, Galois Theory, Third edition, 2003.

Weekly problem sets will be due in class on Friday.

Weekly Syllabus and Homework

Updated February 20, 2025.

Week Date Topics Reading Homework
1 Tue 07 Jan History of solving polynomial equations. The complex numbers and complex conjugation. Field Extensions. Ring theory reminders: PID, UFD, prime and maximal ideals, prime and irreducible elements, fraction fields. Irreducible polynomials and ideals in polynomial rings. DF 9.2
FT 7-11
Thu 09 Jan Roots. Fundamental Theorem of Arithmetic. Reduction mod p. Irreducibility criteria for polynomials. Irreducible polynomials over finite fields. Eisenstein's criterion. Gauss's Lemma and primitive polynomials. DF 9.1-9.5
FT 11-14
2 Tue 14 Jan Finitely generated extensions. Simple extensions. Classification of simple extensions. Transcendental and algebraic elements. Minimal polynomial. DF 13.1-13.2
FT 16-21
Problem Set #1
Thu 16 Jan Tower law for degrees. Algebraic extensions, continued. DF 13.2
FT 14-15, 19-20
3 Tue 21 Jan Compass and straightedge constructions. Constructible numbers form a field. Quadratic closure. Construction impossibility proofs. DF 13.3
FT 22-24
Problem Set #2
Thu 23 Jan Class canceled for jury duty!
4 Tue 28 Jan Quadratic closure. Construction impossibility proofs. Splitting fields. DF 13.3-13.4
FT 22-24,27-30
Problem Set #3
Thu 30 Jan Splitting fields. Embeddings. Counting embeddings. DF 13.4
FT 27-30
Fri 31 Jan Make-up class: Separability. DF 13.5
FT 30-33
5 Tue 04 Feb Frobenius. Perfect fields. Finite fields. Field automorphisms. Automorphism group. Constructing automorphisms. Automorphism group calculations. Fixed fields. DF 14.1-14.2
FT 33-37
Problem Set #4
Thu 06 Feb Galois extensions. Linear independence of embeddings. Fundamental theorem of Galois theory. Examples of the Galois correspondence. Proof of the Galois correspondence. DF 14.1-14.2
FT 37-41
6 Tue 11 Feb Galois group of a polynomial. Normal subgroups of the Galois group. DF 14.1-14.2
FT 35-40,44-45
Takehome Midterm Exam
Thu 13 Feb Normality. Normal closure. Galois is normal and separable. DF 14.1-14.2
FT 37-39
Fri 07 Feb Make-up class: Primitive element theorem (algorithmic and set-theoretic). Cyclotomic fields. Galois theory of finite fields. DF 13.6, 14.3, 14.4, 14.5
FT 53-54, 64-67, 61-63
7 Tue 18 Feb Radical extensions. Solvability by radicals. Solvability by radicals. Galois's solvability theorem. DF 14.7
FT 45-46, 76-77
Thu 20 Feb Discriminant. Galois perspective on quadratic and cubic extensions. Quartic extensions and the cubic resolvent. DF 14.6-14.7
FT 47-52
8 Tue 25 Feb Dedekind's theorem. Computing Galois groups over the rational numbers. Chebotarev density theorem. DF 14.8
FT 55-57
Problem Set #5
Thu 27 Feb Review of modules. Finitely generated modules. Integral elements and equivalent conditions. Integral closure (is a ring). DF 10.1-10.3, 15.3
ANT 25-28
Fri 07 Mar Integrally closed rings. UFD's are integrally closed. Integral closure in finite extensions. Integral ring extensions. Transitivity of integrality. Rings of integers are integrally closed. DF 15.3
ANT 28-30
9 Tue 04 Mar Norm, trace, and discriminant. Integral bases. Rings of integers are finitely generated. Dedekind domains. Prime decomposition in Dedekind domains. ANT 31-36, 48-49
Thu 06 Mar Explicit description of primes lying over. Galois action on primes. Decomposition group. Proof of Dedekind's theorem. ANT 62-65, 144-146
10 Fri 13 Mar Final Exam!



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