User:Selinger

Proposed page: Near ladder escapes

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:

However, there is only one way to prevent the ladder from connecting. Blue must play as follows.

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:

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:

Conversely, if there is less space on the 6th row, Blue has additional ways of blocking the ladder, such as this:

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.

In the above situation, Blue's only winning move is to push.

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:

Note that Blue cannot play move 6 on the 2nd row, or else Red gets a forcing move that allows Red to connect outright:

If Blue plays move 4 at x, then on the next move, Red again has three possiblities:

If Blue plays moves 6 and 8 at y and z (in either order), Red gets a foldback and a switchback:

If Blue plays move 6 at x, Red also gets a foldback and switchback:

In all other cases, Red connects outright.

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

It is fairly common to play the 4th row joseki "C", which leaves the following position in an acute corner:

This position obviously escapes 2nd row ladders. It is perhaps less obvious that it also escapes 3rd row ladders approaching from far enough away:

Note that Red is connected by a 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:

On the other hand, if Blue yields at any point, Red connects by switchback, for example like this:

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:

Red still gets a foldback and a switchback. Instead of 7, Red could have played anywhere in the corner, but since 7 captures the entire corner, it is usually the best move in this situation.

Unused draft material for "Question"

The following was a draft example for the page Question, but it turned out to be too complicated to and not have a good answer.

Example: Template intrusion

Consider the following position, with Blue to move:

Note that Red is connected to the edge by edge template V2b, as highlighted. Blue would like to intrude into this template to gain strength either on the left or on the right.

Blue would like a 4th row ladder escape on the left. But the problem is that if Blue plays at d9 or c10, Red can reconnect by playing a minimaxing move at h7, which strenghtens Red's position.

Blue would also like a 4th row ladder escape on the right. But again, the problem is that if Blue moves at g10 or g9, Red can reconnect at g8, or by playing a minimaxing move, say at b10:

Neither of these outcomes is great for Blue. Instead, what Blue can do is ask the template a question:

Basically, the question is: "How do you want to reconnect?" And based on the answer, Blue will be able to gain some strength on the left or on the right, without giving Red quite as much territory as would otherwise have been the case.

For example, if Red reconnects at e8, then Blue can play e10:

Now Red's mustplay region consists of the 6 highlighted cells. If Red plays at d9, Blue gets a forcing move at b10, giving Blue a 4th row escape on the left, without Red getting g8. If Red plays at d10, g8, or g10, Blue gets a forcing move at d9, giving Blue a 4th row escape on the left without Red getting g8. If Red plays at g9, Blue defends the bridge at f9 and then plays as before. Finally, if Red plays at f10, Blue can respond at g8, getting a 4th row escape on the right. Although Red can still reconnect at b10, taking away Blue's ladder escape on the left, Red does not have the option of getting g8.

To be continued... and simplified?

To do

Add other illustrative examples, such as a template intrusion that forces the player to trade-off between a stronger connection and letting the opponent get a ladder escape, etc.