Cutting right through a knight's move is very big

  Difficulty: Beginner   Keywords: Shape, Proverb

The proverb cutting right through a knight's move is very big is related to the idea of the split shape.

BobMcGuigan: The split knight's move, as in the following diagram:

[Diagram]
Split knight's move  

is usually a very bad shape for Black, but it often happens as a result of a ko threat that was ignored (see e.g. There are No Ko Threats in the Opening).
This shape is also discussed in Four basic shapes, part of a book by the chinese pro Fan Hui, where it is referred to as a ripped keima.

Black might have the knight's move shape already in place, and a ko starts somewhere else on the board. Then White might play W1 as a ko threat, Black might end the ko, and White could then play the stone marked with a square..

[Diagram]
corner  



Two ways to cut the knight's move

  1. strike at the waist of the keima
  2. atekomi
[Diagram]
Trying to cut a keima  

Karl Knechtel: The keima (knight's move) usually provides a reasonably fast way of extending and in general won't be cut. After a strike at the waist of the keima, cutting on the other side isn't possible immediately because the opponent can be caught in a ladder:

(Note that the actual "strike at the waist of the keima" proverb refers to the situation where there's a supporting black stone - see the page for details. It came to mind, though.)

Of course, with two moves in a row locally, Black can plough straight through. The idea behind my proverb is that doing so is usually a very big play in actual game situations, and thus B1 is sente and a big ko threat in many cases.

Why?

[Diagram]
Black is permitted to cut  

When Black is permitted to cut, the damage is evident, though contrived.

  • White is denied a connection between groups above and below (in the given diagram - the 'knight' is 'standing up'), which White previously was entitled to.
  • Black is granted a connection between groups to the left and right which Black previously was not entitled to.
  • White's stones are placed badly; they're touching a stronger black group, and trying to support one white group lets Black target the other.

See also BQM23.


[Diagram]
Add one stone and ...  

While locally the keima is quite strong, it takes only the marked black stone to ensure the cut - Yomiuri Shimbun's English language The Magic of Go column #179 is [ext] an article ([ext] wayback machine) on this. -- lavalyn 17k



Cutting right through a knight's move is very big last edited by 70.184.40.86 on May 11, 2023 - 17:07
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