MathDB
Interlaced polygons

Source: 2021 Czech-Polish-Slovak Match, P3

August 3, 2021

Problem Statement

For any two convex polygons P1P_1 and P2P_2 with mutually distinct vertices, denote by f(P1,P2)f(P_1, P_2) the total number of their vertices that lie on a side of the other polygon. For each positive integer n4n \ge 4, determine max{f(P1,P2)  P1 and P2 are convex n-gons}. \max \{ f(P_1, P_2) ~ | ~ P_1 ~ \text{and} ~ P_2 ~ \text{are convex} ~ n \text{-gons} \}. (We say that a polygon is convex if all its internal angles are strictly less than 180180^\circ.)
Josef Tkadlec (Czech Republic)