Chiyotsui

Chiyotsui (from Japanese, literally "door hinge") is a logic puzzle published by Nikoli. A rectangular or square grid is divided into regions. The goal is to blacken some cells of a grid according to the following rules:

• Black cells form areas. Each area spans exactly two regions, its parts are symmetrical with respect to the region border.
• A cell with a number indicates how many cells in the region must be blackened.
• No two black areas may share an edge.

Cross+A can solve puzzles from 3 x 3 to 30 x 30.