Problem

Source: Romania TST 1 2010, Problem 1

Tags: pigeonhole principle, combinatorics proposed, combinatorics



Given an integer number $n \geq 3$, consider $n$ distinct points on a circle, labelled $1$ through $n$. Determine the maximum number of closed chords $[ij]$, $i \neq j$, having pairwise non-empty intersections. János Pach