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MathNet 2009-part-03 — 175 problems (EN–VI) Question 169

Math Olympiad Vault · MathNet 2009-part-03 — 175 problems (EN–VI)

Question 169

a) In this country there are $1024$ cities, numbered with integers from $0$ to $1023$;
b) Two cities with numbers $m$ and $n$ are connected by a single road if and only if the binary notations of $m$ and $n$ differ in exactly one digit;
c) During the tourist's trip in that country, $8$ roads will be closed for repairing.

Prove that the tourist can organize a closed path by working roads of the Compland which passes through every city exactly once.