Parallel ladder

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A parallel ladder is a situation in which the attacker can make two ladders on top of each other.

2nd and 4th rows

In game

Consider the following position with Red to play.


abcdefghij12345678910

All of Red's pieces form a connected group. This group is connected to the top. At the bottom, Red has a second row ladder with no possible ladder escape on the left. The potential escapes on the right are inadequate. For example, suppose Red ladders to f9. Then tries to escape with

5. h9 g9
6. h8 g8
7. h7 f7.

abcdefghij123456789107651432

Now Red's only reasonable try is 8.g7 f8. Now 9.g6 loses to 9...f5 and 9.h5 loses to the forcing sequence 9...g6 10.h6 h4 11.g5 f5. All the other escape attempts likewise fail. Is Red done for?

No! Red can create a sufficient escape by making use of a parallel ladder. In the original position Red plays 1.e7. How can Blue stop Red from connecting to the bottom? d9 lets Red two-chain from e7 to f8 connecting to the bottom; e9 and e10 allow d9 which is connected to the bottom and threatens to connect to Red's big group through c9 and e8; d10 loses to e8, f9 (forced), c10; hence, Blue is forced to play the parallel ladder move 1...e8. It is simplest for Red to repeat this and ladder to f7 forcing the 2...f8 response.


abcdefghij12345678910

Now Red now goes back to the second row ladder and tries to escape. What have we gained by preceding this with the parallel ladder moves? When trying to escape, the threat to connect to d7-e7-f7 is stronger than the previous weak threat to connect to d7. This extra threat will let us push our escape chain farther up the board and in this case, just far enough to win the game.

Red's winning sequence is long but rather simple because every one of Blue's replies is forced. As before, Red ladders to f9 and escapes with 7. h9. Play continues 7...g9 8.h8 g8 9.h7 g7 10.h6 g6 11.h5. Red is threatening to play g5 with the double winning threats f5 and f6. But if Blue blocks this, say with 11...g5, then Red continues 12.i3 i2 13.h3 h2 and 14.g3 completes the win.

Conceptualisation

Here are presented the essential features of the parallel lader trick on 2nd and 4th row.

The star marked fields must be connected to the top edge.


Note that every blue move is forced. In the following diagram, the threat is connecting to bottom edge with a ziggurat.


1324

135792468

65432

Finally Red is assured to connect to top edge.


321

3rd and 5th rows

It is possible to use this trick off from one row farther back; i.e. with ladders on the third and fifth row but this occurs far less frequently and one has to examine some additional defensive possibilities. Consider the following position.


abcdefghij12345678910

Red has just played e6 trying the parallel ladder trick. With the closer ladder on the second row, we saw that Blue was forced to respond with the parallel ladder play e7. But here Blue has two additional possibilities e8 and c9 (the only other possibility where Red doesn't have a way to force his group to connect to the bottom is c10. But Red can respond with f8 and now Blue has nothing better than e7, g6).

e8 yields a second row ladder after d8, e7, c8, c10, d9. The play c9 also leads to a second row ladder after the likely f7, f8, e8 (d9 is met by e7) d10. In the latter case, Red could again try the parallel ladder trick by playing g7. Of course, the presence of other pieces in the area can change the possibilities.


For whom who understand The parallel ladder trick ! This trick is useful only for ladder 2nd and 4th!

A parallel ladder trick puzzle

Consider the following position with Red to play.


abcdefghij12345678910

The solution is 1.f8 (this is, essentially, Tom's move). Let's see what are Blue's options.

Blue plays 2.d9

2.d9 3.e7 makes easy connection with edge template IIIa


abcdefghij12345678910312

Blue plays 2.e8

2.e8 is not better : 3.c9 4.c10 5.d9 6.d10 7.e9 8.e10 9.g9 connects through edge template III2b linking to bottom.


abcdefghij12345678910235746

Blue plays 2.e9

2.e9 is the best move in almost all situations like this, but it does not work here: 3.c9 4.c10 5.d9 6.d10 7.g7.

Group g7,f8 is connected to bottom thanks to edge template IV2b. And it is connected to the big group with either f6 or e8


abcdefghij12345678910735246

Red 3.c9 could not be e7 nor d9 ... try to think why.