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\def\gotha{\mathfrak{a}}
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\def\gothm{\mathfrak{m}}
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Chapter 3 Cohomology of groups
In this chapter, we introduce the cohomology of finite groups, which plays a key role in the proofs of class field theory. We also discuss homology and Tate groups, and touch briefly on profinite groups.
We begin with the construction of group cohomology in the language of derived functors. Readers not familiar with this material may find it easiest to treat Section 3.1 as a “black box” on first reading.