Difference between revisions of "Switchback"

From HexWiki
Jump to: navigation, search
(A3 switchback)
(2nd-to-6th row switchback: Clarified that the 2-to-6 switchback gives a cascading ladder.)
Line 77: Line 77:
 
== 2nd-to-6th row switchback ==
 
== 2nd-to-6th row switchback ==
  
Perhaps surprisingly, giving enough space, it is possible for the attacker in a 2nd row ladder to force a switchback to a ladder on the 6th row, ''without the help of any additional pieces''. Red can initiate this maneuver by playing the piece marked 5 in the following diagram. The cells marked "*" are not required for this trick (i.e., they may be occupied by Blue).
+
Perhaps surprisingly, giving enough space, it is possible for the attacker in a 2nd row ladder to force a switchback to a [[Theory_of_ladder_escapes#Second_and_fourth_row_cascading_ladders|cascading ladder]] on the 4th and 6th rows, ''without the help of any additional pieces''. Red can initiate this maneuver by playing the piece marked 5 in the following diagram. The cells marked "*" are not required for this trick (i.e., they may be occupied by Blue).
 
<hexboard size="6x11"
 
<hexboard size="6x11"
 
   coords="hide"
 
   coords="hide"
 
   contents="E *:i1 E *:j1 E *:j2 E *:k1 E *:k2 E *:k3 R 1:a5 B 2:a6 R 3:b5 B 4:b6 R 5:g3"
 
   contents="E *:i1 E *:j1 E *:j2 E *:k1 E *:k2 E *:k3 R 1:a5 B 2:a6 R 3:b5 B 4:b6 R 5:g3"
 
   />
 
   />
This position is complicated to analyze, with many possible lines of play, but it can be shown that the following sequence is [[optimal play|optimal]] for both Red and Blue. In other words, Blue cannot prevent Red from getting the switchback, and Red cannot do better (within the amount of space shown here) than getting a ladder on the 6th row.  
+
This position is complicated to analyze, with many possible lines of play, but it can be shown that the following sequence is [[optimal play|optimal]] for both Red and Blue. In other words, Blue cannot prevent Red from getting the switchback, and Red cannot do better (within the amount of space shown here) than getting a cascading ladder on the 4th and 6th row.  
 
<hexboard size="6x11"
 
<hexboard size="6x11"
 
   coords="hide"
 
   coords="hide"
   contents="E *:i1 E *:j1 E *:j2 E *:k1 E *:k2 E *:k3 R 1:a5 B 2:a6 R 3:b5 B 4:b6 R 5:g3 B 6:d5 R 7:e3 B 8:d4 R 9:d3 B 10:f4 R 11:e5 B 12:e4 R 13:h2 B 14:f3 R 15:g1 B 16:f2 R 17:f1 B 18:e2 R 19:e1 B 20:d2 R 21:d1 B 22:c2 R 23:c1"
+
   contents="E *:i1 E *:j1 E *:j2 E *:k1 E *:k2 E *:k3 R 1:a5 B 2:a6 R 3:b5 B 4:b6 R 5:g3 B 6:d5 R 7:e3 B 8:d4 R 9:d3 B 10:f4 R 11:e5 B 12:e4 R 13:h2 B 14:f3 R 15:g1 B 16:f2 R 17:f1"
 
   />
 
   />
Also note that, while the resulting right-to-left ladder is on the 6th row, it is effectively a 4th row ladder since Red already has a solid edge of pieces on the 2nd row.
+
Also note that, while the resulting right-to-left cascading ladder is on the 4th and 6th rows, it is effectively a 2nd-and-4th row cascading ladder since Red already has a solid edge of pieces on the 2nd row.
  
 
[[Category:Definition]]
 
[[Category:Definition]]

Revision as of 02:22, 14 September 2020

A switchback is a situation in which a ladder moves back two or more rows and changes direction. The attacker is still in control after the switchback. Although it is not always a ladder escape, it often can be and is usually a strong play.

For example, consider the following situation. Assume the piece on d1 is in some way connected to the top.


abcdefgh1234

Red makes a switchback as follows:

abcdefgh123413587246

Now the ladder continues from right to the left on the 4th row:

abcdefgh1234131191210

Note here how Red was able to connect back to the d1 piece. This is not always possible, but even if it isn't, the switchback can be used to create a long line connected to the edge and several rows back from it, a distinct advantage.

A3 switchback

A single piece at a3 (or at the equivalent cell on the opposite site of the board) escapes 2nd row ladders. It can also be used as a 3rd-to-5th row switchback:

119121071358246

Note that at no point in the 3rd row ladder, Blue could have yielded, because Red's piece could have escaped the resulting 2nd row ladder outright.

For an example, see also A3 escape trick.

Additionally, even if some of the corner is occupied by the opponent, a single piece at a3 can still be used as a 2nd-to-4th row switchback (but it does not escape 2nd row ladders in this case, nor serve as a 3rd-to-5th row switchback):

7136524

A4 switchback

We have already seen in the first example above that a single Red piece at a4 (or the equivalent cell on the opposite side of the board) can be used as a 2nd-to-4th row switchback. It also works as a 3rd-to-5th row switchback, as follows:

1357246

Red's piece 7 is connected to the bottom. Play continues:

1311912108

Note that if Blue had instead decided to yield the ladder to the second row at any point, the outcome for Blue would have been worse: in that case, Red can perform a 2nd-to-4th row switchback which reconnects to Red's 3rd row ladder.

1191310258746

A5 switchback

A single Red piece at a5 (or the equivalent cell on the opposite side of the board can be used as a 2nd-to-4th row switchback and as a 3rd-to-5th row switchback. The 2nd-to-4th row switchback works as follows:

913587246

Note that Red's piece 9 is connected to the bottom edge by double threat at the two cells marked "*". Play then continues leftward along the 4th row.

The 3rd-to-5th row switchback works as follows:

13119121013587246

Once again, yielding would not have helped Blue.

2nd-to-6th row switchback

Perhaps surprisingly, giving enough space, it is possible for the attacker in a 2nd row ladder to force a switchback to a cascading ladder on the 4th and 6th rows, without the help of any additional pieces. Red can initiate this maneuver by playing the piece marked 5 in the following diagram. The cells marked "*" are not required for this trick (i.e., they may be occupied by Blue).

51324

This position is complicated to analyze, with many possible lines of play, but it can be shown that the following sequence is optimal for both Red and Blue. In other words, Blue cannot prevent Red from getting the switchback, and Red cannot do better (within the amount of space shown here) than getting a cascading ladder on the 4th and 6th row.

1715161397145812101361124

Also note that, while the resulting right-to-left cascading ladder is on the 4th and 6th rows, it is effectively a 2nd-and-4th row cascading ladder since Red already has a solid edge of pieces on the 2nd row.