On the vanishing of twisted -functions of elliptic curves.
Given a number field Galois over the rational field , and a positive integer prime to the class number of , there exists an abelian extension (of exponent ) such that the -torsion subgroup of the Brauer group of is equal to the relative Brauer group of .
We consider the problem of determining whether a set of primes, or, more generally, prime ideals in a number field, can be realized as a finite union of residue classes, or of Frobenius conjugacy classes. We give necessary conditions for a set to be realized in this manner, and show that the subset of primes consisting of every other prime cannot be expressed in this way, even if we allow a finite number of exceptions.
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