Beautiful Combinatorics from St. Petersburg 1993
Source: Kvant Magazine No. 1 2020, 50th Anniversary, M1397
March 10, 2023
combinatoricspolyhedronKvant
Problem Statement
An ant crawls clockwise along the contour of each face of a convex polyhedron. It is known that their speeds at any given time are not less than 1 mm/h. Prove that sooner or later two ants will collide.Proposed by A. Klyachko