Problem

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Tags: geometry, combinatorics, 3rd edition



Let $S$ be a nonempty set of points of the plane. We say that $S$ determines the distance $d > 0$ if there are two points $A, B$ in $S$ such that $AB = d$. Assuming that $S$ does not contain $8$ collinear points and that it determines not more than $91$ distances, prove that $S$ has less than $2004$ elements.