UNAVOIDABLE INDUCED SUBGRAPHS IN LARGE GRAPHS WITH NO HOMOGENEOUS SETS
Maria Chudnovsky, Ringi Kim, Sang‐il Oum, Paul D. Seymour · 2016
Abstract. An n-vertex graph is prime if it has no non-trivial homogeneous set, that is a set X of vertices (2 ≤ |X | ≤ n−1) such that every vertex not in X is either complete or anticomplete to X. A chain of length t is a sequence of t+1 vertices such that for every vertex in the sequence except the first one, its immediate prede-cessor is its unique neighbor or its unique non-neighbor among all of its predecessors. We prove that for all n, there exists N such that every prime graph with at least N vertices contains one of the following graphs or their complements as an induced subgraph: (1) the graph obtained from K1,n by subdividing every edge once, (2) the line graph of K2,n, (3) the line graph of the graph in (1), (4) the half-graph of height n, (5) a prime graph induced by a chain of length n, (6) two particular graphs obtained from the half-graph of height n by making one side a clique and adding one vertex. 1.