This is part of a tiled floor in my house, surrounding a space where I have removed a broken tile. Each tile has a pattern of sixteen smaller squares, three of which are black. On each tile, one of the black squares is a corner square, one is an edge square and one is an inner square. No two black squares touch, either edge to edge or corner to corner. Although I laid the tiles to produce an apparently random pattern, I made sure that no two black squares touched anywhere, either edge to edge or corner to corner.