Ichigomasu

Ichigomasu is a well-known corner shape in Go that resembles a carpenter’s square, a tool used in woodworking. This life-and-death pattern is often deceptive, appearing alive at first glance but requiring careful reading to determine its true fate.

The shape typically arises during corner invasions or defensive maneuvers, where precise stone placement can mean the difference between life and death. The outcome of the battle often depends on the number of outside liberties available to the group. Depending on the situation, the result can range from the group surviving or dying to more complex outcomes like ko or seki.

Recognizing Carpenter’s Square and understanding how to handle it is a challenging but valuable skill in reading life-and-death problems. It’s one of the most complex classical shapes to study, with numerous nuances and variations that even professional players admit they don’t fully master. Many pros approach it cautiously, often preferring to avoid leaving it unprotected or playing it without careful calculation. While not essential for every player, Carpenter’s Square is a fascinating example of how Go combines geometry, strategy, and foresight, rewarding those who can delve into its intricacies and anticipate the consequences of each move.