239 Open MO, 2018, Senior League, Problem 8
Source: 239 Open MO, 2018, Senior League, Problem 8
April 4, 2023
combinatoricsgraph theory
Problem Statement
Graph becomes planar when any vertex is removed. Prove that its vertices can be properly colored with 5 colors. (Using the four-color theorem without proof is not allowed!)Proposed by D. Karpov