Moonsun ("Moon or Sun") is a logic puzzle invented by Nikoli. A rectangular or square grid is divided into regions. A grid contains black and white circles in some cells. The aim is to draw a single non-intersecting loop. The loop must cross borders of each region exactly twice. In a region the loop must visit either all cells with black circles or all cells with white circles. Regions with visited black circles must alternate with regions, where white circles were visited.
Cross+A can solve puzzles from