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Polish MO 2022 P6

Source: Polish MO 2022 P6

February 12, 2022
combinatoricsgraph theory

Problem Statement

nn players took part in badminton tournament, where nn is positive and odd integer. Each two players played two matches with each other. There were no draws. Each player has won as many matches as he has lost. Prove that you can cancel half of the matches s.t. each player still has won as many matches as he has lost.