Direct Sums: Abelian GroupsExplores the concept of direct sums in abelian groups, emphasizing the universal property and homomorphisms.
Algebra: Chain ComplexesExplores chain complexes, abelian groups, homomorphisms, homology groups, and free abelian groups.
Group CohomologyCovers the concept of group cohomology, focusing on chain complexes, cochain complexes, cup products, and group rings.