Ladder
A ladder is a technique for capturing stones. At each step the attacker reduces the defender's liberties from two to one.[1]
The term ladder may also refer to a ranking system used within clubs. See Club Ladder for details.
Example
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 .
Long ladder
Ladders may span a large part of the board. If for example Black captures the white stone in a ladder with , the ladder will go all over the board if White tries to escape, resulting in the next diagram.
If White tries to escape, the ladder will continue in this way. Of course, as it stands, this is a disaster for White.
But if there had been a white stone at a, White could now capture a stone and would stand to capture more because of all the double ataris that White can play. Such a stone which stops a ladder from working is called a ladder-breaker.
Linguistic note on Chinese
The Chinese term for "ladder", 征子 (zhēng zǐ), came from the term 长征 (cháng zhēng), which means "long march".
Computational complexity of ladders
Marcel Crasmaru and John Tromp proved that the problem of computing ladders belong to the class of
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:
- Ladder-breaker
- broken ladder
- Ladder/reading techniques
- Loose ladder (yurumi shicho)
- Spiral ladder
- Shunt
- Net
- Non Local Move Versus A Local Move
- If you don't know ladders, don't play go
- Capture stones caught in a ladder at the earliest opportunity
- Ladder strategy / Discussion
- Double ladder
- Parallel ladders
- Double threat ladder-maker
- Longest Ladder Problem
- Practicing Reading Out Ladders
- Valentine's day problem
- Ladder exercises
- Driving tesuji
- Ladder oddity
- ladder ko
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.)