Lecture 1: Basics of Group Theory
Definitions, Examples: $\mathbb{Z}, \mathbb{R}, \mathbb{C}, \mathbb{Q}, \mathbb{R}_{>0}, \mathbb{Q}_{>0}, Sym(X), S_n$
Cycle notation
Homomorphisms and isomorphisms and examples.
Examples of Classification Theorems
Lecture 2: Symmetric Groups, group actions and cyclic groups
Symmetric groups: cycle notation, multiplication and cycle decompositions
Direct Products of groups
Group Actions: Definition, Examples: trivial action, $\mathbb{Z}$ acting on $\mathbb{R}, \mathbb{Z}^2$ acting on $\mathbb{R},$ left multiplication and conjugation.
Permutation representations.
Faithful actions and Examples
Subgroups: Defintion and definition of subgroup generated by a set $\langle S\rangle$.
Cyclic Groups and orders of elements.
Lecture 3: Cosets
Cosets of a subgroup, partitions of the group by cosets.
Normal Subgroups
Kernels
Quotient Groups
First Isomorphism Theorem
Lecture 4: Isomorphism theorems
Second, Third and Fourth Isomorphism Theorems
Lecture 5: Parity of Permutations
Transpositions, generators for the symmetric group.
Even and odd permutations, definitions
Alternating Group: Definition, examples in small cases.
Group Actions: Definitions of Kernel, Stabiliser, Orbit
Orbit Stabiliser Theorem
Lecture 6: $A_5$ is simple
Conjugacy Classes and centralisers. Examples in Abelian groups and symmetric groups
The class equation. Proof that $p$-groups have non-trivial centre.
Normal subgroups are unions of conjugacy classes.
Conjugacy classes in $S_5$, complete computation.
Conjugacy classes in $A_5$ and proof that $A_5$ is simple.
Lecture 7: Groups acting on subgroups and cosets
$G$ acts on $G/H$ by left multiplication.
Kernel is the normal core of $H$: the largest normal subgroup contained in $H$.
$G$ acting on subgroups by conjugation.
Automorphism groups, Inner automorphisms and outer automorphism groups
Fixed point properties for $p$-groups
Proof of Cauchy's theorem
Statement of Sylow's theorem
Lecture 8: Proof and Applications of Sylow's theorem
Definition of normaliser of a subgroup
Proof of Sylow's theorem using fixed point properties of $p$-groups.
Soluble groups, examples ($p$-groups)
Applications of Sylow's theorems: Groups of order 30, $pq$, $p^2q^2$, 105 are soluble.
Lecture 9: Direct Products, Commutators and Abelianisations
Definition of Direct products, commutators, commutator subgroups and abelianisation.
Proof that $G$ is normal in $G\times H$ and $G\times H/G \cong H$.
Proof that the abelianisation is the largest abelian quotient of $G$.
Discussion of the fundamental theorem of finitely generated abelian groups.
Lecture 10: Detecting direct products and semi-direct products
Lecture 11: Introduction to Rings
Definition and examples of rings
Examples: $\mathbb{Z}$, Matrix rings, Polynomial rings, Group rings
Lecture 12: Ideals
Properties of ideals, intersections, generation, prime ideals, maximal ideals
Prime ideal iff $R/I$ is an integral domain
Maximal ideal iff $R/I$ is a field
Lecture 13: Euclidean domains and Principal Ideal Domains
Definition of Euclidean domain (ED)
Examples: Fields, $\mathbb{Z}, F[x]$
$\mathbb{Z}[x]$ is not an ED
Definition of Principal ideal domain (PID)
ED implies PID
Definition of divisors and uniques of greatest common divisor using ideals
Lecture 14: Unique Factorisation Domains
Definition of prime and irreducible elements
Definition of unique factorisation domains
$r$ is prime iff $r$ is irreducible in a UFD
Principal ideal domains are unique factorisation domains
Lecture 15: Field of fractions and quadratic integer rings
Definition of quadratic integer rings
Proof units are elements with norm 1
Definition of polynomial rings in many variables
$F[x]$ is a unique factorisation domain
Definition of localisations
Lecture 16: Polynomial rings are unique factorisation domains
Irreducible polynomials over $R[x]$ are irreducible over $F[x]$
A polynomial over $F[x]$ is irreducible over $R[x]$ if the gcd of the coefficients is 1
Proof that the polynomial ring over a unique factorisation domain is a unique factorisation domain
Lecture 17: Modules and Module homomorphisms
Definition of module
Examples: $\mathbb{Z}$ modules are abelian groups, modules over a field are vector spaces
Definition of a submodule
Definition of homomorphism and sets of homomorphisms
Proof the set of module homomorphisms is a module
Lecture 18: Quotient Modules and Free Modules
Definition of Quotient module
Statement of Isomorphism theorems for modules
Finite sums of submodules
Generating sets for modules
Direct products
Definition of Free module and proof of existence
Lecture 19: Free modules, Direct Sum, Direct Prodcut, Zorn's Lemma
Proof of Universal Property
$F(A)\cong M$ for any free module on $A$
Definition of Direct Sum and Direct product
Proof they are different
Discussion of Zorn's Lemma
Proof that every ring has a maximal ideal
Lecture 20: Modules over Principal Ideal Domains
3 Equivalent definitions of Noetherian ring
PIDs are Noetherian
Definition of rank of a module
Rank decreases for submodules of free modules over integral domains
Statement of that any sub module of a free module over a PID is free and has a basis that can be extended
Proof of fundamental theorem of finitely generated modules over PIDs
Lecture 21: Modules over PIDs and Tensor Products
Proof of submodules of free modules over a PID are free.
Discussion of how this fails in general
Discussion of extending scalars
Definition of Tensor product
Several examples
Discussion of universal property of $S\otimes_R M$ as an $S$-module
Lecture 22: Tensor products and universal properties
Proof of universal property of tensor product of $S\otimes_R M$ as an $S$-module
Examples of this universal property
Proof that the tensor product is generated by basic tensors of generators
Definition of bilinear maps
Proof of the universal property that any bilinear map from $M\times N$ gives a unique homomorphism from $M\otimes_R N$
Lecture 23: Associativity of Tensor products
Proof that tensor product is associative and commutative
Proof that tensor product is distributive over direct sum
Proof that tensor products of free modules are free
Definition of the tensor product of two maps
Lecture 24: Exact sequences
Definition of exact sequences
Rephrasing of injective and surjective in terms of exact sequences
Definition and examples of short exact sequences
Statement of the 5-lemma
Lecture 25: The 5-lemma and the functors ${\rm{Hom}}_R(D, -)$ and $D\otimes_R-$
Proof of the 5-lemma for two short exact sequences
Definition of projective modules
Definition and discussion of ${\rm{Hom}}_R(D, -)$ for an $R$-module $D$
Definition and discussion of $D\otimes_R-$ for an $R$-module $D$
Examples to show that they do not take exact sequences to exact sequences
Statement that ${\rm{Hom}}_R(D, -)$ preserves exactness on the left
Statement that $D\otimes_R-$ preserves exactness on the left
Lecture 26: Exactness of ${\rm{Hom}}_R(D, -)$ and $D\otimes_R-$
Proof that ${\rm{Hom}}_R(D, -)$ is left exact and $D\otimes_R-$ is right exact
Equivalence of definitions of projective modules