Who killed the Duke of Densmore?
One day Sherlock Holmes received the visit of his friend Watson, who was asked to investigate on a murder that had gone unsolved for more than ten years. At the time, the Duke of Densmore had been killed by a bomb powerful enough to destroy the castle where he had been living since retirement.
Four-coloring a Dodecahedron
By the Four color theorem, the faces of a dodecahedron are four-colorable; that is, one can pick a color among four for each face in such a way that no two adjacent faces share the same color. But can you find such a coloration?