Switchback - Revision history

Selinger: Added B3-without-C1 switchback

2024-03-18T22:47:54Z

Added B3-without-C1 switchback

Selinger: /* A5 switchback */ Added a5 5-7 switchback.

2022-07-12T01:06:10Z

‎A5 switchback: Added a5 5-7 switchback.

Demer: /* A6 switchback */ gave smaller example

2022-03-07T00:19:17Z

‎A6 switchback: gave smaller example

Selinger: Added more details on the B6 2-to-4 switchback.

2022-03-06T16:45:26Z

Added more details on the B6 2-to-4 switchback.

Demer: /* C4 switchback */ corrected effect of foldback threat

2022-02-04T04:12:32Z

‎C4 switchback: corrected effect of foldback threat

Selinger: /* B5 switchback */ Added b5 2nd-to-4th row switchback

2022-02-04T02:09:41Z

‎B5 switchback: Added b5 2nd-to-4th row switchback

Selinger: Fixed a link

2021-12-27T22:21:20Z

Fixed a link

Selinger: /* A5 switchback */ Added a5 4th-to-6th row switchback

2021-09-17T02:39:46Z

‎A5 switchback: Added a5 4th-to-6th row switchback

Selinger: Re-added C4 switchback with a better example, see talk page.

2021-07-07T00:04:11Z

Re-added C4 switchback with a better example, see talk page.

Demer: /* Specific switchbacks */ removed situation in which Red can just connect down

2021-07-05T21:26:04Z

‎Specific switchbacks: removed situation in which Red can just connect down

@@ Line 198: / Line 198: @@
    />
 -->
 === C5-without-C1 switchback ===

@@ Line 113: / Line 113: @@
    />
 Note that Red is connected to the edge by a [[ladder creation template]]. If Blue tries to yield at any point, Red connects outright by the above 3rd-to-5th row switchback.
 === B5 switchback ===

@@ Line 146: / Line 146: @@
 A piece at a6 can also help a 2nd-and-4th row [[parallel ladder]] connect in situations where there is just not enough room for [[Tom's move]], for example like this:
-<hexboard size="6x8"
+<hexboard size="6x6"
    coords="hide"
    edges="bottom right"
-   contents="R h1 a4 a5 b3 c3 d3 b5 B a6 b4 c4 d4 b6
+   contents="R f1 b3 a4 a5 1:d4 3:e4 5:d2 B b4 a6 2:c5 4:c4"
-            R 1:f4 B 2:e5 R 3:g4 B 4:e4 R 5:f2"
    />
 Note that 5 is connected to the red edge by the [[Interior_template#The_shopping_cart|shopping cart]] template and a [[ziggurat]]. If Blue had played anywhere other than 2 and 4 (possibly after [[intrusion|intruding]] into the ziggurat, which Red defends), Red would have connected even without a6.

@@ Line 139: / Line 139: @@
    edges="bottom right"
    contents="R h1 R a5 B a6 R 1:b5 B 2:b6 R 3:f4 B 4:c5 R 5:d3 B 6:e4 R 7:d5 B 8:d4 R 9:f2
-             B 10:f3 R 11:h2"
+             B 10:f3 R 11:h2  S area(a1,a2,d2,f1)"
    />
-The red stone marked "3" is the unique winning move for Red; in particular, Red cannot push the ladder past "1". After this, Blue has several possible responses, of which only one is shown above. However, Red can complete the switchback (or connect) in all cases.
+The red stone marked "3" is the unique winning move for Red; in particular, Red cannot push the ladder past "1". After this, Blue has several possible responses, of which only one is shown above. However, Red can complete the switchback (or connect) in all cases. The shaded area is not needed for the switchback.
 With the amount of space shown here, a6 is not sufficient to switch back a 3rd row ladder. However, with some additional space, this can be done; see [[#B6 switchback|B6 switchback]] and [[#C6 switchback|C6 switchback]] below.
@@ Line 156: / Line 156: @@
 === B6 switchback ===
-A single Red piece at b6 (or the equivalent cell on the opposite side of the board) can be used as a 2nd-to-4th row switchback for the same reason as [[#A6 switchback|a6]], and can also be used as a 3rd-to-6th row switchback. It Blue does not yield, the 3rd-to-6th row switchback works as follows:
+A single Red piece at b6 (or the equivalent cell on the opposite side of the board) can be used as a 2nd-to-4th row switchback for the same reason as [[#A6 switchback|a6]], using this much space:
 <hexboard size="6x6"
    coords="hide"

@@ Line 78: / Line 78: @@
 === C4 switchback ===
-C4 acts as a [[ladder escape]] for 2nd and 3rd row ladders, as well as for 4th row ladders given enough space on the 5th row. Also, in the presence of a [[Foldback#Foldback_threat|foldback threat]], c4 can acts as a 4th-to-6th row switchback for the same reason as a4. But in cases where there isn't enough space to do any of the above, c4 may still give a (very short) 4th-to-6th row switchback, like this:
+C4 acts as a [[ladder escape]] for 2nd and 3rd row ladders, as well as for 4th row ladders given either enough space on the 5th row or a [[Foldback#Foldback_threat|foldback threat]]. But in cases where there isn't enough space to do either of the above, c4 may still give a (very short) 4th-to-6th row switchback, like this:
 <hexboard size="7x9"

@@ Line 217: / Line 217: @@
    contents="R h2 B h6 R a3 B a4 R 1:b3 B 2:b4 R 3:c3 E a:c4 b:d5 c:b6"
    />
-Note that if Blue had tried to yield at any time prior to move 3, Red could have used the 3rd-to-5th row switchback to connect. After move 3, Blue has only three options, marked "a", "b", and "c". Option "a" is pushing the ladder. Options "b" and "c" prevent Red from getting the switchback, but Red will get a [[foldback underneath]] instead, i.e., a 2nd row ladder going right-to-left (this also serves as a ladder escape fork for any Red 2nd row ladders arriving from the left). So "a" is Blue's best option.
+Note that if Blue had tried to yield at any time prior to move 3, Red could have used the 3rd-to-5th row switchback to connect. After move 3, Blue has only three options, marked "a", "b", and "c". Option "a" is pushing the ladder. Options "b" and "c" prevent Red from getting the switchback, but Red will get a [[foldback|foldback underneath]] instead, i.e., a 2nd row ladder going right-to-left (this also serves as a ladder escape fork for any Red 2nd row ladders arriving from the left). So "a" is Blue's best option.
 <hexboard size="6x10"
    coords="hide"

← Older revision		Revision as of 02:39, 17 September 2021
Line 105:		Line 105:

	Once again, yielding would not have helped Blue.		Once again, yielding would not have helped Blue.
		+
		+	In addition, in the presence of a [[Foldback#Foldback_threat\|foldback threat]], a5 can also be used as a 4th-to-6th row switchback as follows:
		+	<hexboard size="6x8"
		+	coords="hide"
		+	edges="bottom right"
		+	contents="R h2 a6 B b4 R 1:c3 B 2:c4 R 3:d3 B 4:d4 R 5:e3 B 6:e4 R 7:f4 B 8:f3 R 9:g1"
		+	/>
		+	Note that Red is connected to the edge by a [[ladder creation template]]. If Blue tries to yield at any point, Red connects outright by the above 3rd-to-5th row switchback.

	=== B5 switchback ===		=== B5 switchback ===

@@ Line 75: / Line 75: @@
    />
 Of course, Blue cannot yield, or else Red gets the 3rd-to-5th row switchback and connects.
 === A5 switchback ===