MathDB
Crossing ٍٍChords

Source: Iranian Combinatorics Olympiad 2020 P3

April 24, 2020
combinatorics

Problem Statement

13991399 points and some chords between them is given. a)a) In every step we can take two chords RS,PQRS,PQ with a common point other than P,Q,R,SP,Q,R,S and erase exactly one of RS,PQRS,PQ and draw PS,PR,QS,QRPS,PR,QS,QR let ss be the minimum of chords after some steps. Find the maximum of ss over all initial positions. b)b) In every step we can take two chords RS,PQRS,PQ with a common point other than P,Q,R,SP,Q,R,S and erase both of RS,PQRS,PQ and draw PS,PR,QS,QRPS,PR,QS,QR let ss be the minimum of chords after some steps. Find the maximum of ss over all initial positions.
Proposed by Afrouz Jabalameli, Abolfazl Asadi