Galois cohomology, the commutative case
Let k be a field, and let K be a Galois extension of k. The Galois group Gal(K/k) of the extension K/k is a profinite group (cf. Chap. I, §1.1), and one can apply to it the methods and results of Chapter I; in particular, if Gal(K/k) acts on a discrete group A(K), the H q (Gal(K,k),A(K)) are well-defined (if A(K) is not commutative, we assume that q = 0, 1).
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