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MathNet 2008-part-02 — 165 problems (EN–VI) Question 144

Math Olympiad Vault · MathNet 2008-part-02 — 165 problems (EN–VI)

Question 144

Assume that $n \geq 3$ people with different names sit around a round table. We call any unordered pair of them, say $M$ and $N$, dominating, if
(i) $M$ and $N$ do not sit on adjacent seats, and
(ii) on one (or both) of the arcs connecting $M$ and $N$ along the table edge, all people have names that come alphabetically after the names of $M$ and $N$.

Determine the minimal number of dominating pairs.