Named after the traditional carpenter’s steel square (曲尺 / さしがね),Shashigane transforms geometric dissection into pure logical harmony.

Fundamental Principles

• The 1-Cell Rule: No region can be thicker than 1 cell anywhere. No \(2\times 2\) blocks, forks, or cross shapes are allowed.
• One and Only One Bend: Every region must turn 90° exactly once. Straight lines (180° only) or U-shapes (two turns) are strictly illegal.
• Corner Placement: Circle clues are strictly locked to the corner vertex of their respective L-shapes. If you see a circle at the edge of the board, its arms can only extend inward!
• Arrow Alignments: An arrow is always located at an extreme end of an arm and shoots directly into the corner bend. It cannot shoot past the bend.

Solving Techniques

Begin by inspecting corner circles situated near board boundaries. A circle at \((0, 0)\) can only extend down and right. Compare numbered circles with available clearance: if a circle has clue 5 and can only extend 2 cells horizontally, its vertical arm must extend at least 2 cells down. Look for trapped single cells that can only be saved by passing arms!