Stostone ("Stone on Stone") is a logic puzzle invented by Nikoli. A rectangular or square grid is divided into regions. The goal is to blacken some cells of a grid ("stones") according to the following rules: - All black cells in a region must be connected horizontally or vertically. - A cell with a number indicates how many cells in the region must be blackened. - In regions without a number any amount of cells may be blackened (at least one). - When two cells are orthogonally adjacent across a region boundary, at least one cell must be white. - If all stones "fall down", they must cover exactly the bottom half of the grid. mind puzzles for adults - mind puzzle books for adults - mind teasers puzzles for adults - puzzles engage your mind - easy mind puzzles - mind puzzle games for adults - active minds jigsaw puzzles - brain puzzles for adults - brain puzzle books for adults - brain puzzle books - brain teaser puzzles - brain puzzle challenge - brain puzzle games - active minds puzzles