Yunikumaka ("Unique Marker") is a logic puzzle invented by Naoki Inaba (Japan). A rectangular or square grid contains dots; a dot can be situated in the center of a cell or on a border between neighbouring cells. The aim is to divide a grid on regions having the size of exactly four cells (tetromino). Each region contains exactly one dot either in the center of a cell or on a border between cells. Dots on borders between regions are ignored. Black cells do not belong to any region.
Cross+A can solve puzzles from