MathDB
very nice problem

Source: meditranean 2003

March 16, 2009
geometry3D geometryspherecombinatorics unsolvedcombinatorics

Problem Statement

Consider a system of infinitely many spheres made of metal, with centers at points (a,b,c)Z3(a, b, c) \in \mathbb Z^3. We say that the system is stable if the temperature of each sphere equals the average temperature of the six closest spheres. Assuming that all spheres in a stable system have temperatures between 0C0^\circ C and 1C1^\circ C, prove that all the spheres have the same temperature.