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Penny Haxell: Extremal graphs for connectedness

Tid: Ti 2014-04-22 kl 14.00 - 15.00

Plats: Institut Mittag-Leffler, Auravägen 17, Djursholm

Medverkande: Penny Haxell, University of Waterloo

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It is known that the topological connectedness of the independence complex of the line graph of G is bounded below by the matching number of G (minus 2). This parameter turns out to be important for some old conjectures about hypergraphs, in particular Ryser's conjecture on r-partite r-uniform hypergraphs. We study the bipartite graphs G that are extremal for this parameter, and as one consequence characterise the 3-partite 3-uniform hypergraphs that are extremal for Ryser's conjecture.

Joint work with Lothar Narins and Tibor Szabo.