5 people sitting around table
Source: Bulgaria 1978 P3
June 17, 2021
combinatorics
Problem Statement
On the name day of a man there are people. The men observed that of any people there are that knows each other. Prove that the man may order his guests around circular table in such way that every man have on its both side people that he knows.N. Nenov, N. Hazhiivanov