Yajisan-Kazusan

Yajisan-Kazusan is a binary determination logic puzzle published by the Japanese puzzle company Nikoli. It is played on a rectangular grid similar in layout to the puzzle Yajilin, with some cells holding a number and a directional arrow. Each numbered arrow cell claims that a certain count of shaded cells lie along the row or column it points toward, but the puzzle's defining twist is that not every clue is true: some of the numbers are deliberately false, and the solver's task is to work out which. The rules require that shaded cells never touch each other orthogonally, that every unshaded cell forms one single connected region, and that any clue cell whose stated number turns out to be wrong must itself be shaded, at which point it stops constraining the solution. Because a shaded cell cannot be adjacent to another shaded cell, only roughly half the cells in any row or column can be shaded, and solvers use that limit to spot clue numbers that are impossible and therefore false, working outward from those contradictions to complete the grid.