Selinger: Added a3+a5 foldbacks.

2022-07-23T23:25:59Z

Added a3+a5 foldbacks.

Selinger: Created a page on foldbacks.

2021-05-16T01:58:47Z

Created a page on foldbacks.

New page

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):
<hexboard size="5x11"
coords="none"
edges="bottom right"
contents="R h1 B b3 c3 R d1 B e1 R 1:d2"
/>
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:
<hexboard size="5x11"
coords="none"
edges="bottom right"
contents="R h1 B b3 c3 R d1 B e1 R 1:d2 B 2:d3 R 3:e2 B 4:d5 R 5:e3 B 6:f4 R 7:g3 B 8:g4"
/>
However, Red can now get a foldback, namely a 2nd row ladder from right to left:
<hexboard size="5x11"
coords="none"
edges="bottom right"
contents="R h1 B b3 c3 R d1 B e1 R d2 B d3 R e2 B d5 R e3 B f4 R g3 B g4 R 9:d4 B 10:c5 R 11:c4"
/>
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).
<hexboard size="5x8"
coords="none"
edges="bottom right"
contents="R e1 B d1--h1 h2 a3 R f2 R c1 B b3
R 1:c2"
/>
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"
coords="none"
edges="bottom right"
contents="R e1 B d1--h1 h2 a3 R f2 R c1 B b3
R 1:c2 B 2:c3 R 3:d2 B 4:d3 R 5:e2 B 6:f3 R 7:e3 B 8:d5 R 9:d4 B 10:c5 R 11:c4"
/>
Note that Blue cannot yield, because then Red gets a 3rd row ladder, which the 4th row stone does escape.

== 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.

@@ Line 31: / Line 31: @@
 Similarly, consider a single red stone at c4 (or the equivalent cell on the opposite side of the board).
 <hexboard size="5x8"
-    coords="none"
+  coords="none"
    edges="bottom right"
    contents="R e1 B d1--h1 h2 a3 R f2 R c1 B b3
@@ Line 38: / Line 38: @@
 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"
-    coords="none"
+  coords="none"
    edges="bottom right"
    contents="R e1 B d1--h1 h2 a3 R f2 R c1 B b3
@@ Line 44: / Line 44: @@
    />
 Note that Blue cannot yield, because then Red gets a 3rd row ladder, which the 4th row stone does escape.
 == 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.

Foldback - Revision history

Selinger: Added a3+a5 foldbacks.

Selinger: Created a page on foldbacks.