Ladder escape fork

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A forking move which creates a ladder escape.

Example

In the following position, Red has no edge template.

abcdefg1234567

The only option seems to be a ladder.

abcdefg12345671324

However, pushing the ladder too much is useless, and it actually enables Blue to win.

abcdefg1234567135246

Red needs the two pieces at the top right hand-corner of the board. Red pushes the ladder just enough to use a ladder escape fork. Piece number 3 is called the pivot piece. It threatens to connect to the top group and acts as a ladder escape as well.

abcdefg1234567132

When to fork

In all of the above examples, we have shown Red pushing the ladder until Red is two hexes away from the pivot location, and then pivoting. This serves well for illustration purposes, as it makes it more obvious why the pivot piece is forcing. However, in practice, it is often unnecessary, and sometimes detrimental, to start by pushing the ladder. Instead, Red can often (but not always) play the pivot piece right away.

2nd row ladder

In the case of 2nd row ladders, pushing the ladder before pivoting usually does not hurt the attacker, and can sometimes be necessary. For example, consider this situation, with Red to move:

ab

In this situation, Red must push the ladder all the way to "a" before pivoting at "b", or else the pivot does not work.

3rd row ladder

In the case of a 3rd row ladder, pushing the ladder before pivoting is sometimes necessary, for the same reason as for 2nd row ladders. However, in situations where pushing the ladder is not necessary, the attacker may gain a small advantage from not pushing the ladder. Consider the following situation, which frequently develops near an obtuse corner in actual games. With Red to move:

cabx

Red threatens a 3rd row ladder at "a", and would like to pivot at "b" to climb to "c". Red can indeed do this, but the problem is that if Red starts by pushing the ladder, Blue gets an additional forcing move at "x":

987163245

On the other hand, if Red pivots without first pushing the ladder, Red can still climb to "c", but Blue does not get the forcing move. This confers a small but potentially significant advantage on Red.

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See also