12 colors fro 12-gon - All-Russian MO 1995 Regional (R4) 9.4
Source:
August 26, 2024
combinatoricsColoringcombinatorial geometry
Problem Statement
Every side and diagonal of a regular -gon is colored in one of given colors. Can this be done in such a way that, for every three colors, there exist three vertices which are connected to each other by segments of these three colors?