Ladder

Path: <= Tesuji =>
  Difficulty: Introductory   Keywords: Tesuji, Go term

The term ladder may also refer to a ranking system used within clubs. See Club Ladder for details.

Chinese 1: 征子 (zhēng zǐ)
Chinese 2: 征 (zhēng);
Chinese 3: 扭羊头 (niǔ yáng tóu)
Japanese 1: シチョウ (shichō)
Japanese 2: 征 (shichō) (Rare)
Korean: 축/逐 (chuk)






A ladder is a technique for capturing stones. At each step the attacker reduces the defender's liberties from two to one.[1]

There are plenty of Ladder problems and exercises in Sensei's Library.

Table of contents Table of diagrams
Ladder
Playing out the ladder
A long ladder
A long ladder (cont'd)
A long ladder with ladder breaker
A broken ladder
More complicated ladder
Straight ladder

Example

[Diagram]
Ladder  

Black B1 starts a ladder to capture the white+circle stone.

[Diagram]
Playing out the ladder  

If White tries to escape, Black can at each time play atari and White will be captured.

Clearly White should see this and not play W2.

Longer ladder

[Diagram]
A long ladder  

Ladders may span a large part of the board. If for example Black captures the white stone in a ladder with B1, the ladder will cross the entire board if White tries to escape, resulting in the next diagram.

[Diagram]
A long ladder (cont'd)  

If White tries to escape, the ladder will continue in this way. This is a disaster for White.


Ladder breaker

[Diagram]
A long ladder with ladder breaker  

Suppose, however, that there is a stone in the path of the ladder, such as white+circle in this diagram,

[Diagram]
A broken ladder  

After W8, B5 is suddenly in atari. Now, black cannot continue with the ladder, because white could simple capture a stone. The ladder is broken. Also, note that black's formation is full of cutting points each of which is a double atari that White can play. This is therefore a disaster for Black.

And so we can plainly see that a ladder is little more than a one-sided fight for one side or the other. Hence the proverb, "If you don't know ladders, don't play go".


Theoretical ladder

Although ladders normally follow a zigzag pattern across the board, and indeed derive their name from this "stairway" like formation, any sequential series of atari's forcing the opponents stones around is considered a ladder. Thus ladders may go straight, or bend, and still be considered ladders.

[Diagram]
More complicated ladder  

In this example, there are several white (white+circle) and black (black+circle) stones in the path of the ladder. The diagram shows that white cannot escape with W1. Had black followed the basic zigzag pattern by playing B4 at W5, white would have escaped. But by using his own additional stones for support, black is able to maneuver the ladder past white's stones.

[Diagram]
Straight ladder  

In the same vein, this pattern is also a ladder, though most people might not refer to it as such.


Linguistic note on Chinese

The Chinese term for "long march", 长征 (cháng zhēng), is often used as a metaphor for the Chinese term for "ladder", 征子 (zhēng zǐ). The idea is that if the ladder is played out fully, then it can be a very long sequence, like a long march.

According to John Fairbairn, the word 征 first appeared in Chapter 2 of Dunhuang Classic in the 6th century, well before Mao Zedong's time, and there is no reference there to marches. In the ancient, 征 refers to firmly attacking a rebellious state and had nothing directly to do with marching, but later it developed to another meaning of "(military) expedition".

Computational complexity of ladders

Marcel Crasmaru and John Tromp proved that the [ext] problem of computing ladders belongs to the class of [ext] PSPACE-complete, due to the possible twists and turns and other complications in the execution of a ladder. However, such complicated cases are quite rare in Go. The majority of the ladders can be easily read out by a beginner with some practice. (A similar comment applies to many such proofs. Indeed, they are "asymptotic" and really only apply to arbitrarily large boards. By themselves they say nothing about our good old 19x19 goban. Concrete bounds are needed for that.)


See also:

Homonym


[1] The term, "ladder", though long in use, is also debatable. The term "stair" is much better to describe this form. (But... A stair and not a ladder, a thing and not a process? It's a reckless path to disaster, not a trip to the attic.)


Path: <= Tesuji =>
Ladder last edited by 91.54.40.243 on November 2, 2012 - 15:27
RecentChanges · StartingPoints · About
Edit page ·Search · Related · Page info · Latest diff
[Welcome to Sensei's Library!]
RecentChanges
StartingPoints
About
RandomPage
Search position
Page history
Latest page diff
Partner sites:
Go Teaching Ladder
Goproblems.com
Login / Prefs
Tools
Sensei's Library