China MO 2023 P3
Source: China MO 2023 P3
December 29, 2022
combinatorics
Problem Statement
Given positive integer , color the points of the regular -gon in black and white, in black and in white.
The coloring distance of two black points is defined as the smaller number of white points in the two paths linking the two black points.
The coloring distance of two white points is defined as the smaller number of black points in the two paths linking the two white points.
We define the matching of black points : label the black points with satisfying no intersects inside the gon.
We define the matching of white points : label the white points with satisfying no intersects inside the gon.
We define .
Prove that: