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On k-leaf powers

Tuesday 4th September 2007 - 12:10 to 12:30
INI Seminar Room 1

In 2002, Nishimura, Ragde and Thilikos introduced the notion of k-leaf power and k-leaf root, motivated by the following: ``... a fundamental problem in computational biology is the reconstruction of the phylogeny, or evolutionary history, of a set of species or genes, typically represented as a phylogenetic tree ...''. The species occur as leaves of the phylogenetic tree. Let G=(V_G,E_G) be a finite undirected graph. For k at least 2, a tree T is a $k$-leaf root of G if V_G is the leaf set of T and two vertices x,y in V_G are adjacent in G if and only if their distance d_T(x,y) in T is at most k. The graph G is a $k$-leaf power if it has a k-leaf root. Obviously, a graph is a 2-leaf power if and only if it is the disjoint union of cliques, i.e., it contains no induced path of three vertices. Recent work on leaf powers contains characterisations of 3- and 4-leaf powers and their variants. It is well known that every k-leaf power is a strongly chordal graph. For k at least 6, no characterisation of $k$-leaf powers and no efficient recognition is known. We discuss some open problems and new results on leaf powers.

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University of Cambridge Research Councils UK
    Clay Mathematics Institute London Mathematical Society NM Rothschild and Sons