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Consider the real plane $\mathbb{R}^2$. Does there exist a subset $S$ of the real plane, such that every line $l$ in $\mathbb{R}^2$ intersects $S$ at exactly one point?

user107952
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1 Answers1

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No.

Given $2$ distinct points $\mathbf{x}, \mathbf{y} \in S \subseteq \mathbb{R}^2$, consider the line $\ell$ that passes through $\mathbf{x}$ and $\mathbf{y}$. So $S$ can contain at most $1$ point. Obviously, $S \neq \varnothing$, so consider the cases where $|S| = 1$. It's easy to construct a line that misses the given point.

Sammy Black
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