Difference between revisions of "1964 IMO Problems/Problem 4"

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Revision as of 19:34, 15 July 2009

Problem

Seventeen people correspond by mail with one another - each one with all the rest. In their letters only three different topics are discussed. Each pair of correspondents deals with only one of these topics. Prove that there are at least three people who write to each other about the same topic.

Solution

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