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2021 China MO P5 -- A Neat Graph Theory Problem

Source: 2021 China Mathematical Olympiad P5

November 25, 2020
graph theorycombinatoricspolyhedronEvenParity

Problem Statement

PP is a convex polyhedron such that:
(1) every vertex belongs to exactly 33 faces.
(1) For every natural number nn, there are even number of faces with nn vertices.
An ant walks along the edges of PP and forms a non-self-intersecting cycle, which divides the faces of this polyhedron into two sides, such that for every natural number nn, the number of faces with nn vertices on each side are the same. (assume this is possible)
Show that the number of times the ant turns left is the same as the number of times the ant turn right.