Lecture
This lecture covers the Hopf formula in cohomology groups, focusing on the 4-term exact sequence and the Hopf formula theorem. It explains the concepts of kernel, subgroup, and conjugation, leading to the identification of the cohomology groups. The lecture delves into the Hopf formula's implications and applications, illustrating the isomorphism between different groups and the significance of exact sequences in cohomology. It concludes with a discussion on homology with arbitrary coefficients and the relationship between group actions and cohomology.