Carathéodory Number of P 3 -Convexity of Claw-Free Graphs

Abstract

Given a connected simple undirected graph G = ( V , E ) , a subset S of V is P 3 -convex if each vertex of G not in S has at most one neighbor in S . The P 3 -convex hull ⟨ S ⟩ of S is the smallest P 3 -convex set containing S . A Carathéodory set of G is a set S ⊆ V such that ⟨ S ⟩ ∖ ⋃ w ∈ S ⟨ S ∖ { w } ⟩ is non-empty. The Carathéodory number of G , denoted by C ( G ) , is the largest cardinality of a Carathéodory set of G . In this paper, we settle the conjecture posed by Barbosa et al. appeared in [SIAM J. Discrete Math. 26 (2012) 929–939] in the affirmative, which states that for a claw-free graph G of order n ( G ) , the Carathéodory number C ( G ) of the P 3 -convexity satisfies C ( G ) ≤ 2 n ( G ) + 6 5 . Furthermore, we determine all graphs attaining the bound.