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(462) 7

Part of 1995 Tournament Of Towns

Problems(1)

TOT 462 1995 Spring S A7 common acquaintances in group of 50 people

Source:

7/9/2024
Prove that in a group of 5050 people there are always two who have an even number (possibly zero) of common acquaintances within the group.
(SI Tokarev)
combinatorics