The Sylvester–Gallai Theorem

24 points - 07/31/2026

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Comments

hyperhello today at 2:42 AM
> Every finite set of points in the Euclidean plane that is not collinear has a line that passes through exactly two of the points.

I can't make out the point here (no pun). Of course a line can pass through any two points. It could pass through three if those points were collinear but the statement says they're not. So what is the new fact?

Nail2680 today at 3:25 AM
I might be too stupid to understand why this is interesting and useful. If it helps I am a working physicist, and a lot of pure math is lost on me. I think I followed this, but I don't know why one would care or this would be interesting.
emil-lp today at 2:00 AM
Futility closet is fantastic!
stackghost today at 4:11 AM
>Every finite set of points in the Euclidean plane that is not collinear has a line that passes through exactly two of the points.

Isn't this a tautology?

The problem definition states that the set of points is in Euclidean space, which from Euclid's Axioms means we can draw a line between any two points. The set of points is defined to be not collinear, thus we cannot draw a line passing through more than two of them. This is just simple logic.