SE-SKOLORNAS 1985 Problem 6
X-wich has a vibrant club-life. For every pair of inhabitants there is exactly one club to which they both belong. For every pair of clubs there is exactly one person who is a member of both. No club has fewer than members, and at least one club has members. How many people live in X-wich?
Dataset text AI-MO AoPS. Quoted with source.
Solutions
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