MathDB
Hard combinatorics with team nominated based on three rankings

Source: Germany 2023, Problem 3

June 16, 2023
combinatoricscombinatorics proposedgraph theoryTournamentTournament graphs

Problem Statement

For a competition a school wants to nominate a team of kk students, where kk is a given positive integer. Each member of the team has to compete in the three disciplines juggling, singing and mental arithmetic. To qualify for the team, the n2n \ge 2 students of the school compete in qualifying competitions, determining a unique ranking in each of the three disciplines. The school now wants to nominate a team satisfying the following condition:
()(*) If a student XX is not nominated for the team, there is a student YY on the team who defeated XX in at least two disciplines.
Determine all positive integers n2n \ge 2 such that for any combination of rankings, a team can be chosen to satisfy the condition ()(*), when
a) k=2k=2, b) k=3k=3.