(also known as " ") is a logic puzzle invented by Naoki Inaba (Japan). It consists of a grid, with numbers in some cells. The aim is to blacken some cells of a grid according to the following rules: • The white cells form a single island. Each numbered cell must be a part of this island. • The numbers indicate how many unnumbered white cells can be reached from that cell by moving horizontally or vertically. Numbered cells block access.