unit disk covering

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May 17

there are four points on the plane. if any three points (of the four) can be covered by a unit disk, then all four points can be covered by a unit disk.

10:35 AM | Blog it

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	jinwrote: Kevin: maybe i didn't state the problem carefully. Any three points merely need to be covered by a unit disk: they are not necessarily on the rims of the the disk. i cannot exactly follow the contradiction you suggested. it would be great if u could give me a bit more details. btw, how's everything going? May 20
	Kevin Lauwrote: En? This looks like an obvious fact and the proof is straightforward: Arbitrarily pick on a unit circle 3 points and the 4th point outside of the circle. It is easy to show by contradiction that there must exists two points on the circle such that they and the 4th point cannot be covered by a unit disk. May 17

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