Given are two polyominos, the first one is an L-shape consisting of three squares, the other one contains at least two squares. Prove that if n and m are coprime then at most one of the n×n and m×m boards can be tiled by translated copies of the two polyominos.Proposed by: András Imolay, Dávid Matolcsi, Ádám Schweitzer and Kristóf Szabó, Budapest komalcombinatoricstilings