party acquaintances
Source: Swiss 2002
October 12, 2006
combinatorics unsolvedcombinatorics
Problem Statement
In a group of people, every weekend someone organizes a party in which he invites all of his acquaintances. Those who meet at a party become acquainted. After each of the people has organized a party, there still are two people not knowing each other. Show that these two will never get to know each other at such a party.