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第12手斷（傳統斷在a位）

**飛刀定式**是一類圍棋定式的統稱，因後續分支綿長複雜，對弈雙方爭奪激烈而得名。

它由Tromp-Taylor規則下的零知識圍棋AI發現，人類棋手深入研究的一類星位定式，是圍棋發展到AI時代發現的最大型的定式。

定式特點
----

1. 複雜定式

據統計截至2019年3月前後共計有680余種分支。
目前對其變化分支仍然沒有簡明的結論，且分支數量仍在增加之中。與之相比，人類棋手發現的複雜定式在分支數量上遠少於該定式。

2. 全局定式

該定式弈至羋氏飛刀時，往往會將棋盤鋪陳過半，其他三個角部的子力配置亦影響定式的變化發展。

3. 胜负优先

AlphaGo發現並推廣應用的星位佈局和三三入侵手段，推動了人類棋手對星定式中點三三變化的深入研究。

Facebook的ElfOpenGo項目與2019年2月釋出的權重會在高算力的情況下高頻使用羋氏飛刀。

雖然AlphaGo公開資料與對弈情況中並未出現該定式，隨着公開可獲得的圍棋AI進展，LeelaZero項目出現了與AlphaGo選擇避開定式的相同走法。LeelaZero從ElfOpenGo公開棋譜中習得該定式並超過Elf系列權重，至266號權重會在普通算力情況下（1600 playouts）大量使用該定式並且以此定式在同算力情況(大於100k計算量)下擊敗KataGo G170系列的20B權重。

含有額外圍棋領域知識的AI:KataGo目前沒有獨立發現該定式。由於使用目數策略，使得KataGo對後續變化的探索傾向較低，不熟悉該定式變化。這一認知情況與人類棋手對該定式的認識過程類似。

定式研究與發展
-------

1. 小目騙招


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圖1 小目演變

小目定式之一，一般當作騙招教學。

在1989年首屆應氏杯對局中，聶衛平决赛對戰曹薰铉五番棋中，第二、第五局使用定式的前几手，到黑7時，曹執黑挺頭(a位長)，没有選擇該變化。聶認爲開局沒必要下的激烈，於自己的棋風有利。

2. 星位場合着法


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圖2 星位演變

三三入侵小飛應後，黑7退長硬封白棋

20世紀80年代，黑5小飛應三三入侵開始流行，當時棋手認爲黑棋擋住就很不錯了，沒必要過早開展波及全局的戰鬥。較早發動爭奪是不通棋理的表現。

3. AI研究


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圖3 小飛後托扳

AI時代引發了職業棋手對星定式的研究熱潮，其中三三侵角後的短手數AI定式獲得了棋手認同與實戰應用。

當黑5小飛，白在徵子有利的情況下，採用白6二路托（AlphaGo有此時脫先的處理）。

羋氏飛刀是飛刀定式中穩定出現的棋型，其後的變化最爲複雜難解（參見LeelaZ晉升譜20200219）。羋氏飛刀是人類棋手在AI研究的基礎上領先公開AI一步發現的定式。

羋氏飛刀
----

羋氏飛刀是19路圍棋中，飛刀定式的大型變化分支。當飛刀定式走至防守方外扳時，該棋型稱爲羋氏飛刀。其後對弈雙方爭奪激烈，棋盤鋪陳過半仍然勝負難解。

羋昱廷對飛刀定式的深入研究與實戰應用成果，大大推動了棋壇對飛刀定式的認識和使用，並使羋氏飛刀成爲人類圍棋棋手對抗AI圍棋棋手的重要手段。

在2018年8月1日中國名人戰半決賽，芈昱廷執白對童夢成的比賽中，星位點三三的定式下出了扳的新手(下圖第20手)，其後整個黑角被吃，甚至造成當時在野狐圍棋分析情勢的絕藝 AI 誤判角落的對殺。之後這一手及其後的變化在職業比賽中流行，被媒體命名為「芈氏飛刀」。

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| 第20手外扳即為芈氏飛刀，以前的下法通常是虎在a的位置 |

該變化在次月即2018年9月，引發了職業棋手的研究熱潮和實戰應用。雖然2017年7月李世乭在農心盃已經下出斷打（不走20扳而在b位斷）。但羋昱廷對外扳棋型的深入研究和職業賽中的實戰成果，及至業餘網路圍棋中流行後，中國棋壇稱"小羋飛刀""羋氏飛刀"，簡稱"羋刀"。羋氏飛刀作爲飛刀定式最大型的變化，往往有混用指稱的情況。

簡化處理
----

由於飛刀定式變化非常複雜，難以把握，棋手要避免弈至羋刀棋型的複雜大型爭奪的局面，可以採取以下定式避開。

### 避開飛刀定式


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圖4 退長

AlphaGo在ELO5125之後，在應對二路托時，均選擇長出，避免了複雜的飛刀定式，LeelaZero有同樣的選擇趨勢。可見防守一方避免通過一個角部的爭奪而決定全盤勝負。

### 選擇簡明變化


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圖5 黑17粘（或在b位虎）

黑棋25手也可脫先或與a位打吃。

黑17粘上簡明定型，防守方獲得外勢的同時，棄掉的1、3、13三子以後可以作爲劫材。AlphaGo Teach中有此變化。b位虎回到傳統變化，均製造了劫材庫。

參考來源
----


1. ↑ . github.com.  [2020-02-20]. （原始内容存档于2020-10-16）.
2. ↑ . github.com.  [2020-03-04]. （原始内容存档于2020-10-16）.
3. ↑ . www.101weiqi.com.  [2020-02-20]. （原始内容存档于2020-10-16）.
4. ↑ . www.101weiqi.com.  [2020-02-20]. （原始内容存档于2020-10-16）.
5. ↑ . senseis.xmp.net.  [2020-02-20]. （原始内容存档于2021-01-26）.
6. ↑ . zero.sjeng.org.  [2020-02-20]. （原始内容存档于2020-10-16）.
7. ↑  腾讯野狐围棋.. weiqi.qq.com.  [2018-09-28]. （原始内容存档于2020-05-23）.
8. ↑ . m.sohu.com.  [2018-09-28]. （原始内容存档于2020-05-23）.
9. ↑ . www.huibangqyh.cn.  [2020-02-20]. （原始内容存档于2021-12-28）.
10. ↑ . www.alphago-games.com.  [2020-02-20]. （原始内容存档于2020-10-16）.