Problem
The Problem
At a party of people, each pair either has met or hasn't. Prove that there are always two people at the party with the same number of acquaintances (i.e., same degree in the acquaintance graph).
At a party of people, each pair either has met or hasn't. Prove that there are always two people at the party with the same number of acquaintances (i.e., same degree in the acquaintance graph).