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Signature des unités cyclotomiques et parité du nombre de classes des extensions cycliques de ${\bf Q}$ de degré premier impair
If K is an abelian extension of odd degree of Q, the study of the 2-class group (in the usual sense) of K (and even the study of the parity of the class number h of K) is difficult and the algorithms which are knowned concern principally the case [K:Q]=3.