2n people sit, knowing both neighbors in a round table
Source: Czech-Polish-Slovak Junior Match 2018, Team p5 CPSJ
March 7, 2020
combinatorics
Problem Statement
There are people () sitting around the round table, with each person getting to know both with his neighbors and exactly opposite him sits a person he does not know. Prove that people can rearrange in such a way that everyone knows one of their two neighbors.