Difference between revisions of "Foldback"
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Similarly, consider a single red stone at c4 (or the equivalent cell on the opposite side of the board). | Similarly, consider a single red stone at c4 (or the equivalent cell on the opposite side of the board). | ||
<hexboard size="5x8" | <hexboard size="5x8" | ||
| − | + | coords="none" | |
edges="bottom right" | edges="bottom right" | ||
contents="R e1 B d1--h1 h2 a3 R f2 R c1 B b3 | contents="R e1 B d1--h1 h2 a3 R f2 R c1 B b3 | ||
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This stone can serve as a 4th-to-2nd row foldback, even in situations, such as the one shown here, where it would not normally escape a 4th row ladder. | This stone can serve as a 4th-to-2nd row foldback, even in situations, such as the one shown here, where it would not normally escape a 4th row ladder. | ||
<hexboard size="5x8" | <hexboard size="5x8" | ||
| − | + | coords="none" | |
edges="bottom right" | edges="bottom right" | ||
contents="R e1 B d1--h1 h2 a3 R f2 R c1 B b3 | contents="R e1 B d1--h1 h2 a3 R f2 R c1 B b3 | ||
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/> | /> | ||
Note that Blue cannot yield, because then Red gets a 3rd row ladder, which the 4th row stone does escape. | Note that Blue cannot yield, because then Red gets a 3rd row ladder, which the 4th row stone does escape. | ||
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| + | === A3+A5 foldback === | ||
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| + | Consider red stones at a3 and a5 (or the equivalent cells on the opposite side of the board). | ||
| + | <hexboard size="5x7" | ||
| + | coords="none" | ||
| + | edges="bottom right" | ||
| + | contents="R g1 g3" | ||
| + | /> | ||
| + | Red can use this to get a foldback from the 4th to the 2nd row: | ||
| + | <hexboard size="5x7" | ||
| + | coords="none" | ||
| + | edges="bottom right" | ||
| + | contents="R g1 g3 R a2 B a3 R b2 B b3 R 1:c2 B 2:c3 R 3:d2 B 4:e4 R 5:d3 B 6:c5 R 7:c4" | ||
| + | /> | ||
| + | If Blue plays somewhere other than 4 or 6 (in either order), Red connects outright. | ||
| + | |||
| + | Moreover, Red can also use this to get a foldback from the 5th to the 3rd row: | ||
| + | <hexboard size="5x7" | ||
| + | coords="none" | ||
| + | edges="bottom right" | ||
| + | contents="R g1 g3 R a1 B a2 R b1 B b2 R c1 B c2 R 1:d1 B 2:d2 R 3:e1 B 4:e2 R 5:f1 B 6:e4 R 7:f2 B 8:f5 R 9:e3" | ||
| + | /> | ||
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| + | The same two stones can even be used for a 6th-to-4th row foldback: | ||
| + | <hexboard size="6x7" | ||
| + | coords="none" | ||
| + | edges="bottom right" | ||
| + | contents="R g2 g4 R a1 B a2 R b1 B b2 R c1 B c2 R 1:d1 B 2:d2 R 3:e1 B 4:e3 R 5:e2 B 6:d4 R 7:d3" | ||
| + | /> | ||
== Foldback threat == | == Foldback threat == | ||
We say that a ladder carries a ''foldback threat'' if getting a foldback would allow the attacker to connect. Even if the attacker cannot actually get the foldback, the mere ''threat'' of a foldback can be an advantage for the attacker. An example is the [[Switchback#A4_switchback|4th-to-6th row switchback using A4]], which only works in the presence of a foldback threat. | We say that a ladder carries a ''foldback threat'' if getting a foldback would allow the attacker to connect. Even if the attacker cannot actually get the foldback, the mere ''threat'' of a foldback can be an advantage for the attacker. An example is the [[Switchback#A4_switchback|4th-to-6th row switchback using A4]], which only works in the presence of a foldback threat. | ||
Latest revision as of 23:25, 23 July 2022
A foldback, also known as folding under or a foldback underneath, is a situation in which a ladder changes direction and turns into a ladder closer to the edge. The attacker is still in control after the foldback. A foldback is not to be confused with a switchback, in which the ladder changes direction and continues further from the edge.
Foldbacks are only possible from 4th row ladders or higher, as there is not enough space under a 3rd row ladder to fold back.
Examples
D5 foldback
Suppose Red has a 4th row ladder approaching a red stone at d5 (or the equivalent cell on the opposite side of the board):
In this situation, the stone on the 5th row does not act as a ladder escape. For example, Blue can block the ladder as follows:
However, Red can now get a foldback, namely a 2nd row ladder from right to left:
If Red has some way of escaping this ladder, Red connects.
C4 foldback
Similarly, consider a single red stone at c4 (or the equivalent cell on the opposite side of the board).
This stone can serve as a 4th-to-2nd row foldback, even in situations, such as the one shown here, where it would not normally escape a 4th row ladder.
Note that Blue cannot yield, because then Red gets a 3rd row ladder, which the 4th row stone does escape.
A3+A5 foldback
Consider red stones at a3 and a5 (or the equivalent cells on the opposite side of the board).
Red can use this to get a foldback from the 4th to the 2nd row:
If Blue plays somewhere other than 4 or 6 (in either order), Red connects outright.
Moreover, Red can also use this to get a foldback from the 5th to the 3rd row:
The same two stones can even be used for a 6th-to-4th row foldback:
Foldback threat
We say that a ladder carries a foldback threat if getting a foldback would allow the attacker to connect. Even if the attacker cannot actually get the foldback, the mere threat of a foldback can be an advantage for the attacker. An example is the 4th-to-6th row switchback using A4, which only works in the presence of a foldback threat.
