All you need to know about Carpenter's Square
Doing Life & Death exercises is one of the best ways to improve Go-playing skills. In this series of articles, I will cover all the Life & Death problems around so-called Carpenter's Square and its related shapes. In Chinese literature, this is called Jin Gui Jiao (金柜角 or 'gold cabinet corner' if translated literally).
Such corner shapes, while having little rooms inside, can contain endless variations. Once in an interview a Chinese female professional was asked how she would handle such corner shapes. The answer was along the lines of "I would fortify it if I am leading, otherwise I would hide my head in the sand". Perhaps only top professionals can really understand every details around these shapes.
I studied these corner shapes many years ago. I compiled 31 shapes and 100+ variations and published them on an old Chinese version of Go4Go.net around 2003. The shape classification roughly follows what's shown in Cho Chikun's Life and Death Dictionary with the order adjusted and additional shapes introduced. The solution are based on many life & death books I've read over the years, and my own studies.
This series of articles are unusual because they discuss practical situations. In strict life & death problem solving, people will prefer creating a ko to settling in a seki. But the latter may well be the correct decision in real games. Wherever applicable, I always try to compare different solutions and give practical advice.
Each time I review these materials I find new variations which I've neglected before. Over the next few weeks, I will revisit these shapes, add more diagrams and comments, and translate everything into English. I wish I can learn something new through this process and hope you enjoy reading these articles.