LARGE -FREE SUBGRAPHS IN -CHROMATIC GRAPHS

Abstract

AbstractFor a graph G and a family of graphs $\mathcal {F}$ , the Turán number ${\mathrm {ex}}(G,\mathcal {F})$ is the maximum number of edges an $\mathcal {F}$ -free subgraph of G can have. We prove that ${\mathrm {ex}}(G,\mathcal {F})\ge {\mathrm {ex}}(K_r, \mathcal {F})$ if the chromatic number of G is r and $\mathcal {F}$ is a family of connected graphs. This result answers a question raised by Briggs and Cox [‘Inverting the Turán problem’, Discrete Math.342(7) (2019), 1865–1884] about the inverse Turán number for all connected graphs.