MathDB
15th ibmo - venezuela 2000/q1.

Source: Spanish Communities

April 15, 2006
modular arithmeticcombinatorics unsolvedcombinatorics

Problem Statement

A regular polygon of n n sides (n3 n\geq3) has its vertex numbered from 1 to n n. One draws all the diagonals of the polygon. Show that if n n is odd, it is possible to assign to each side and to each diagonal an integer number between 1 and n n, such that the next two conditions are simultaneously satisfied: (a) The number assigned to each side or diagonal is different to the number assigned to any of the vertices that is endpoint of it. (b) For each vertex, all the sides and diagonals that have it as an endpoint, have different number assigned.