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Named after Jacques Herbrand and Kenneth Ribet.
Etymology from Wiktionary, CC BY-SA 4.0.
Herbrand-Ribet theorem
Today it means: A result on the class group of certain number fields, strengthening Ernst Kummer's theorem to the effect that the prime p divides the class number of the cyclotomic field of p-th roots of unity iff p divides the numerator of the n-th Bernoulli number Bₙ for some n, 0 < n < p − 1. The Herbrand–Ribet theorem specifies what, in particular, it means when p divides such an Bₙ. Full definition →