Demer: /* D5 does not escape a 4th row ladder */ presumably this "Red" should've been "Blue"

2023-11-25T10:27:38Z

‎D5 does not escape a 4th row ladder: presumably this "Red" should've been "Blue"

Selinger: New page

2023-01-08T01:59:48Z

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There are a number of [[ladder]] situations where a player does not technically have a [[ladder escape]], but in practice often ends up escaping the ladder anyway. This usually happens because the opponent must play extremely precisely in order to prevent the ladder from escaping, and can easily miss the correct move. In such cases, we may speak of a '''near ladder escape'''.

This pages lists some common near ladder escapes, and how to thwart them.

== C4 does not escape a 5th row ladder ==

A single stone at c4 (or the equivalent cell on the opposite side of the board) does not escape a 5th row ladder, even when there is a certain amount space on the 6th row as shown here:
<hexboard size="6x11"
edges="bottom right"
coords="none"
visible="area(a6,k6,k1,f1)"
contents="R i3 1:e2 B d3 f1 g1"
/>

However, there is only one way to prevent the ladder from connecting. Blue must play as follows.
<hexboard size="6x11"
edges="bottom right"
coords="none"
visible="area(a6,k6,k1,f1)"
contents="R i3 1:e2 B d3 f1 g1 B 2:e3 R 3:f2 B 4:h4"
/>
In this situation, 2 followed by 4 is the only winning sequence for Blue. The best Red can do is the following, which is not sufficient to connect Red's ladder:
<hexboard size="6x11"
edges="bottom right"
coords="none"
visible="area(a6,k6,k1,f1)"
contents="R i3 e2 B d3 f1 g1 B e3 R f2 B h4 R 5:h3 B 6:i4 R 7:g4 B 8:g3 R 9:f3 B 10:e5 R 11:j2 B 12:f4 R 13:h1 B 14:g2"
/>
Note that Red gets a 5th-to-3rd row [[foldback]], so if Red escapes a 3rd row ladder moving left, Red connects.

Also note that Red would be able to connect if the stone to the left of 13 were not occupied. Therefore, with slightly more space on the 6th row, a single stone at c4 actually does escape a 5th row ladder:
<hexboard size="6x11"
edges="bottom right"
coords="none"
visible="area(a6,k6,k1,f1)"
contents="R i3 1:e2 B d3 f1"
/>
Conversely, if there is less space on the 6th row, Blue has additional ways of blocking the ladder, such as this:
<hexboard size="6x11"
edges="bottom right"
coords="none"
visible="area(a6,k6,k1,f1)"
contents="R i3 1:e2 B d3 f1 g1 h1 B 2:e3 R 3:f2 B 4:f3 R 5:g2 B 6:h3 R 7:g3 B 8:f5 R 9:g4 B 10:g6"
/>

== D5 does not escape a 4th row ladder ==

A single stone at D5 (or the equivalent cell on the opposite side of the board) does not escape a 4th row ladder, even when the 6th row is empty as shown here. However, the situation is still very threatening. Red gets both a [[foldback]] and a [[switchback]].
<hexboard size="6x12"
edges="bottom right"
coords="none"
visible="area(a6,l6,l1,f1)"
contents="R i2 1:d3 B c4"
/>
In the above situation, Blue's only winning move is to [[ladder handling|push]].
<hexboard size="6x12"
edges="bottom right"
coords="none"
visible="area(a6,l6,l1,f1)"
contents="R i2 1:d3 B c4 B 2:d4 R 3:e3 E x:e4 y:f5 z:d6"
/>
For move 4, Blue has three possible choices: x, y, or z. If Blue plays moves 4 and 6 at y and z (in either order), Red gets a foldback and a switchback, but does not connect outright:
<hexboard size="6x12"
edges="bottom right"
coords="none"
visible="area(a6,l6,l1,f1)"
contents="R i2 1:d3 B c4 B 2:d4 R 3:e3 B 4:f5 R 5:f4 B 6:d6 R 7:e5 B 8:e6 R 9:d5 B 10:c6 R 11:h4 B 12:g4 R 13:h2 B 14:f3 R 15:g1"
/>
Note that Blue cannot play move 6 on the 2nd row, or else Red gets a forcing move that allows Red to connect outright:
<hexboard size="6x12"
edges="bottom right"
coords="none"
visible="area(a6,l6,l1,f1)"
contents="R i2 1:d3 B c4 B 2:d4 R 3:e3 B 4:f5 R 5:f4 B 6:e5 R 7:e4 B 8:d5 R 9:h4 B 10:g4 R 11:h2"
/>
If Blue plays move 4 at x, then on the next move, Red again has three possiblities:
<hexboard size="6x12"
edges="bottom right"
coords="none"
visible="area(a6,l6,l1,f1)"
contents="R i2 1:d3 B c4 B 2:d4 R 3:e3 B 4:e4 R 5:f3 E x:g4 y:g5 z:e6"
/>
If Blue plays moves 6 and 8 at y and z (in either order), Red gets a foldback and a switchback:
<hexboard size="6x12"
edges="bottom right"
coords="none"
visible="area(a6,l6,l1,f1)"
contents="R i2 1:d3 B c4 B 2:d4 R 3:e3 B 4:e4 R 5:f3 B 6:g5 R 7:g4 B 8:e6 R 9:f5 B 10:f6 R 11:e5 B 12:d6 R 13:i4 B 14:h4 R 15:j3 B 16:g3 R 17:h1"
/>
If Blue plays move 6 at x, Red also gets a foldback and switchback:
<hexboard size="6x12"
edges="bottom right"
coords="none"
visible="area(a6,l6,l1,f1)"
contents="R i2 1:d3 B c4 B 2:d4 R 3:e3 B 4:e4 R 5:f3 B 6:g4 R 7:f4 B 8:e6 R 9:e5 B 10:d6 R 11:f5 B 12:f6 R 13:h5 B 14:g5 R 15:h3 B 16:g3 R 17:h1"
/>
In all other cases, Red connects outright.

'''Climbing.''' If Red lacks both a switchback threat and a foldback threat, Red's goal may be to deny Blue a ladder escape in the corner, and to [[climbing|climb]] as far as possible. Red can play as follows:
<hexboard size="9x12"
edges="bottom right"
coords="none"
visible="area(a9,l9,l1,i1)"
contents="R i5 1:d6 B c7 B 2:d7 R 3:e6 B 4:e7 R 5:f6 B 6:g8 R 7:g7 B 8:g6 R 9:f7 B 10:e9 R 11:j7 B 12:i7 R 13:j6 B 14:i6 R 15:j5 B 16:h6 R 17:i4 B 18:h4 R 19:j2"
/>
Or if Blue plays a different move 12, Red can even do this:
<hexboard size="9x12"
edges="bottom right"
coords="none"
visible="area(a9,l9,l1,i1)"
contents="R i5 1:d6 B c7 B 2:d7 R 3:e6 B 4:e7 R 5:f6 B 6:g8 R 7:g7 B 8:g6 R 9:f7 B 10:e9 R 11:j7 B 12:h7 R 13:k4 B 14:j6 R 15:i7 B 16:i6 R 17:l5 B 18:h6 R 19:i4 B 20:h4 R 21:k1"
/>

== Joseki "C" does not escape a 4th row ladder ==

It is fairly common to play the [[Joseki#4th_row_josekis|4th row joseki]] "C", which leaves the following position in an acute corner:
<hexboard size="5x11"
edges="bottom right"
coords="none"
visible="area(a5,k5,k1,e1)"
contents="R h3 i2 B i3"
/>
This position obviously escapes 2nd row ladders. It is perhaps less obvious that it also escapes 3rd row ladders approaching from far enough away:
<hexboard size="5x11"
edges="bottom right"
coords="none"
visible="area(a5,k5,k1,e1)"
contents="R h3 i2 B i3 B b4 R 1:c3 B 2:c4 R 3:d3 B 4:d4 R 5:f2 B 6:e3 R 7:e2 B 8:f4 R 9:f3 B 10:e4 R 11:g5 S area(c3,b5,h5,h3,i2,i1,g1)"
/>
Note that Red is connected by a [[Interior_template#The_span|span]], and the connection only requires the shaded area. The "magic" move is 5. If Red just continues to push on the 3rd row, Red does not connect.

Does the above corner position escape a 4th row ladder? If Blue naively keeps pushing the ladder, then Red does indeed connect:
<hexboard size="5x11"
edges="bottom right"
coords="none"
visible="area(a5,k5,k1,e1)"
contents="R h3 i2 B i3 B c3 R 1:d2 B 2:d3 R 3:e2 B 4:e3 R 5:f2 B 6:f3 R 7:h1"
/>
On the other hand, if Blue [[ladder handling|yields]] at any point, Red connects by [[switchback]], for example like this:
<hexboard size="5x11"
edges="bottom right"
coords="none"
visible="area(a5,k5,k1,e1)"
contents="R h3 i2 B i3 B c3 R 1:d2 B 2:d3 R 3:e2 B 4:e4 R 5:e3 B 6:d4 R 7:g3 B 8:f3 R 9:g1"
/>
Indeed, for a 4th row ladder approaching the corner, there is only one possible Blue move that prevents Red from escaping the ladder. This "magic move" is 4 in the following diagram:
<hexboard size="5x11"
edges="bottom right"
coords="none"
visible="area(a5,k5,k1,e1)"
contents="R h3 i2 B i3 B c3 R 1:d2 B 2:d3 R 3:e2 B 4:f4 R 5:f3 B 6:d5 R 7:j1 B 8:g3 R 9:h1"
/>
Red still gets a [[foldback]] and a [[switchback]]. Instead of 7, Red could have played anywhere in the corner, but since 7 [[captured cell|captures]] the entire corner, it is usually the [[optimal play|best move]] in this situation.

== See also ==

* [[Ladder escape]]
* [[Switchback]]
* [[Foldback]]

[[Category:Advanced Strategy]]
[[Category:Ladder]]

@@ Line 74: / Line 74: @@
    contents="R i2 1:d3 B c4 B 2:d4 R 3:e3 B 4:f5 R 5:f4 B 6:e5 R 7:e4 B 8:d5 R 9:h4 B 10:g4 R 11:h2"
    />
-If Blue plays move 4 at x, then on the next move, Red again has three possiblities:
+If Blue plays move 4 at x, then on the next move, Blue again has three possiblities:
 <hexboard size="6x12"
    edges="bottom right"

Near ladder escape - Revision history

Demer: /* D5 does not escape a 4th row ladder */ presumably this "Red" should've been "Blue"

Selinger: New page