A note on Erdős's mysterious remark

Abstract

We give an alternative proof of the statement, by using elimination from algebraic geometry, that the only set $S\subset {\mathbb{R}}^2$, $\left|S\right|=6$ such that all subsets that form a triangle are isosceles triangles, is the regular pentagon with its center. Our proof can be extended to answer some related questions raised by Erdős.

7 pages, 3 figures