Edited by R. T. Curtis
Edited by R. A. Wilson
Publisher: Cambridge University Press
Print Publication Year: 1998
Online Publication Date:May 2010
Chapter DOI: http://dx.doi.org/10.1017/CBO9780511565830.019
For every finite group G and every prime p, ip(G) ≤ 3, where ip(G) denotes the smallest number of Sylow p-subgroups of G whose intersection coincides with the intersection of all Sylow p-subgroups of G. For all simple groups (G, ip(G) ≤ 2.
Let G be a finite group and p be a prime. Denote by Op(G) the intersection of all Sylow p-subgroups of G and by ip(G) the smallest number i such that Op(G) is equal to the intersection of i Sylow p-subgroups. Obviously, ip(G) = 1 if and only if G has an unique Sylow p-subgroup. J. Brodkey  proved that ip(G) ≤ 2 if a Sylow p-subgroup of G is abelian and N. Ito  found sufficient conditions for a finite solvable group to satisfy ip(G) ≤ 2.
This paper discuss some recent results in this direction. The main theorems are the following:
Theorem 1  If G is a simple non-abelian group then ip(G) = 2 for every prime p dividing the order of G.
Theorem 2  For every finite group G and every prime p, ip(G) ≤ 3.
Section 2 contains a sketch of a proof of Theorem 1 which uses the Classification of Finite Simple Groups. Section 3 presents results about intersections of Sylow subgroups in arbitrary finite groups. We use the notation of the atlas .
The following elementary results, the first of which is trivial, give a base for induction arguments in the proof of the main theorems of this paper.