On a Koolen -- Park inequality and Terwilliger graphs

2010/07/20 by Alexander Gavrilyuk, Gavrilyuk, Alexander
Mathematics · #Combinatorics (math.CO) #FOS: Mathematics #math.CO

paper · pdf · doi:10.48550/arxiv.1007.3339

arxiv created 2010/07/20 · arxiv updated 2010/07/21

Abstract

J.H. Koolen and J. Park have proved a lower bound for intersection number c₂ of a distance-regular graph Γ. Moreover, they showed that the graph Γ which attains the equality in this bound is a Terwilliger graph. We prove that Γ is the icosahedron, the Doro graph or the Conway-Smith graph, if equality is attained and c₂≥ 2.

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