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Product decompositions of quasirandom groups and a Jordan type theorem

Nikolay Nikolov, László Pyber (2011)

Journal of the European Mathematical Society

We first note that a result of Gowers on product-free sets in groups has an unexpected consequence: If k is the minimal degree of a representation of the finite group G , then for every subset B of G with | B | > | G | / k 1 / 3 we have B 3 = G . We use this to obtain improved versions of recent deep theorems of Helfgott and of Shalev concerning product decompositions of finite simple groups, with much simpler proofs. On the other hand, we prove a version of Jordan’s theorem which implies that if k 2 , then G has a proper subgroup...

Quand seule la sous-somme vide est nulle modulo p

Jean-Marc Deshouillers (2007)

Journal de Théorie des Nombres de Bordeaux

Soit c > 1 , p un nombre premier et 𝒜 une partie de / p de cardinal supérieur à c p telle que pour tout sous-ensemble non vide de 𝒜 , on a b b 0 . On montre qu’il existe s premier à p tel que l’ensemble s . 𝒜 est très concentré autour de l’origine et qu’il est presque entièrement composé d’éléments de partie fractionnaire positive. Plus précisément, on a a 𝒜 s a p < 1 + O ( p - 1 / 4 ln p ) et a 𝒜 , { s a / p } 1 / 2 s a p = O ( p - 1 / 4 ln p ) . On montre également que les termes d’erreurs ne peuvent être remplacés par o ( p - 1 / 2 ) .

Recognition of characteristically simple group A 5 × A 5 by character degree graph and order

Maryam Khademi, Behrooz Khosravi (2018)

Czechoslovak Mathematical Journal

The character degree graph of a finite group G is the graph whose vertices are the prime divisors of the irreducible character degrees of G and two vertices p and q are joined by an edge if p q divides some irreducible character degree of G . It is proved that some simple groups are uniquely determined by their orders and their character degree graphs. But since the character degree graphs of the characteristically simple groups are complete, there are very narrow class of characteristically simple...

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