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Joseki is an English loanword from Japanese, usually referring to standard sequences of moves played out in a corner that result in a locally even exchange. The term may also be used for sequences that occur in other parts of the board (sides and center) and at various stages in the game (opening, middle, and end), although such usage is usually made using explicit wording, such as endgame joseki. It is also possible, although uncommon, to use the term joseki to refer to sequences whose outcome is not equal.
Which sequences are considered playable joseki has changed throughout history, owing to the effects of rule changes (most notably komi), continued research from professional players, and, most recently, from artificial intelligence analysis. A joseki that has fallen out of fashion is normally labelled as "old" or "bad." If a sequence is not considered joseki, it usually means that either one side (of the exchange) is left at a clear disadvantage with little or no redeeming benefits, or that the position is too uncommon to have developed an agreed upon continuation. Proper evaluation of joseki considers the trade-offs between: sente and gote, territory and influence, speed and solidity, local and global balance, and aji.
Due to the numerous amount of researched joseki and the fact that joseki may occur at any part of the board and at any stage in the game, books and resources on joseki have largely focused on one "category" of joseki at a time. The main categories include: corner joseki, opening joseki, middlegame and side joseki, and endgame joseki. Many of these categories may further be broken up into subcategories, such as the avalanche joseki, Chinese opening, and middle game reduction play. Two special categories of joseki study are trick plays and hamete.
The English term joseki comes from the Japanese 定石 (jōseki). The second character 石 (seki), literally "stone," refers to "sequence" or "moves" here. The first character 定 (jō) has a range of meanings. However, the relevant meaning (in this case) is "(pre-)established". The Korean word, when written in hanja, uses the same characters, and has the same semantics as the Japanese word. The Chinese word uses a different second character, 式, which can be expressed in English as "pattern" or "form."
Below is a quick reference to navigate through the main branches of corner joseki, where navigation is performed by clicking on the letters in the diagram.
- a: 3-4 joseki (komoku)
- b: 4-4 joseki (hoshi)
- c: 3-3 joseki (sansan)
- d: 3-5 joseki (mokuhazushi)
- e: 4-5 joseki (takamoku)
- f: 6-3 joseki (omokuhazushi)
- g: 6-4 joseki (otakamoku)
- h: 5-5 joseki (gonogo)
- AlphaGo Joseki - Joseki seen in AlphaGo games.
- Joseki Choice - Making in-game decisions about which joseki to play.
- Joseki Discussions – 101 discussion about joseki.
- Joseki Pages – List of many joseki pages in SL. Mainly centered around user discussion and a question/answer format.
- Joseki Resources – List of many resources to study joseki, including online, printed and software.
- Overview of Joseki – List of corner patterns in outline format.