DE-BUNDESWETTBEWERB 2021 Problem 6
A school has 2021 students, each of which knows at least 45 of the other students (where "knowing" is mutual).
Show that there are four students who can be seated at a round table such that each of them knows both of her neighbours.
Dataset text AI-MO AoPS. Quoted with source.
Official text: Bundeswettbewerb Mathematik 2021 official paper, page 1.
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