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Principalization algorithm via class group structure

Daniel C. Mayer (2014)

Journal de Théorie des Nombres de Bordeaux

For an algebraic number field K with 3 -class group Cl 3 ( K ) of type ( 3 , 3 ) , the structure of the 3 -class groups Cl 3 ( N i ) of the four unramified cyclic cubic extension fields N i , 1 i 4 , of K is calculated with the aid of presentations for the metabelian Galois group G 3 2 ( K ) = Gal ( F 3 2 ( K ) | K ) of the second Hilbert 3 -class field F 3 2 ( K ) of K . In the case of a quadratic base field K = ( D ) it is shown that the structure of the 3 -class groups of the four S 3 -fields N 1 , ... , N 4 frequently determines the type of principalization of the 3 -class group of K in N 1 , ... , N 4 . This provides...

Principe d’Heisenberg et fonctions positives

Jean Bourgain, Laurent Clozel, Jean-Pierre Kahane (2010)

Annales de l’institut Fourier

On décrit un problème naturel concernant la transformation de Fourier. Soient f , f ^ deux fonctions associées par celle-ci, positives pour x a et nulles en zéro. Quelle est la borne inférieure pour a  ? En dimension supérieure, même question, l’intervalle étant remplacé par la boule de rayon a . On montre l’existence d’une borne inférieure strictement positive, qui est estimée en fonction de la dimension. La dernière section montre que cette question est naturellement liée à la théorie des fonctions zêta....

Probabilistic construction of small strongly sum-free sets via large Sidon sets

Andreas Schoen, Tomasz Srivastav, Anand Baltz (2000)

Colloquium Mathematicae

We give simple randomized algorithms leading to new upper bounds for combinatorial problems of Choi and Erdős: For an arbitrary additive group G let P n ( G ) denote the set of all subsets S of G with n elements having the property that 0 is not in S+S. Call a subset A of G admissible with respect to a set S from P n ( G ) if the sum of each pair of distinct elements of A lies outside S. Suppose first that S is a subset of the positive integers in the interval [2n,4n). Denote by f(S) the number of elements in a...

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