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Rev

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$\begingroup$ Nice! After thinking about your proof that this works, I thought of a different formulation of it. reveal spoilerPut a car in each city, and think of this as being in positions -10, -8, -6, ..., 8, 10 relative to Rome, where positive is clockwise and negative is counterclockwise. As the cars move, adjust their positions up or down by 1. Since all cars have the same parity, two cars can't switch signed positions without meeting, and once they meet, they're stuck together. So if car -10 and 10 both meet at 0, every car which was between them must be at 0 as well. $\endgroup$

Misha Lavrov
– Misha Lavrov

2026-03-30 21:53:51 +00:00
Commented yesterday
$\begingroup$ @MishaLavrov yes, it makes the clearer that that police cars will indeed collect all cars. $\endgroup$

Florian F
– Florian F

2026-03-31 06:16:34 +00:00
Commented 22 hours ago

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