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en:group:seminars:20070308 [2009/04/07 11:17] external edit
en:group:seminars:20070308 [2016/06/23 11:26] (current)
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 ==== abstract ==== ==== abstract ====
 The zig-zag is a graph product enabling the recursive construction The zig-zag is a graph product enabling the recursive construction
 +of explicit expander families. These graphs are remarkable in that
 +the proof of expansion relies on combinatorial rather than
 +algebraic arguments, and is considerably simpler than that of 
 +other known constructions.
 +We will first present the zig-zag product, its expansion
 +properties and the constructions it yields. We will then
 +explore the link with the semi-direct product of
 +groups, which was used to show that expansion of Cayley
 +graphs is not a group property (i.e. it depends on the
 +choice of generators).