Difference between revisions of "Intrusion"
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| − | # | + | An '''intrusion''' is a move that threatens to disconnect a [[virtual connection]] of the opponent. The most common kind of intrusion is a '''template intrusion''', which is a move inside the carrier of one of the opponent's [[templates]]. |
| + | |||
| + | By definition, a template or a virtual connection can always be defended, and therefore, intruding into a template does not actually disconnect the opponent (unless the opponent [[tenuki|declines]] to defend the template). Nevertheless, a well-played intrusion can be to the benefit of the intruding player. For example, the intruding player may gain a bit of [[territory]] or a [[ladder escape]]. | ||
| + | |||
| + | Choosing which one of several possible intrusions is the most advantageous is one of the most difficult skills in Hex. | ||
| + | |||
| + | == Examples == | ||
| + | |||
| + | === Bridge intrusion === | ||
| + | |||
| + | The most basic template is the [[bridge]]. It has two potential intrusions: at A or at B. | ||
| + | <hexboard size="3x2" | ||
| + | coords="none" | ||
| + | edges="none" | ||
| + | visible="area(b1,a2,a3,b2)" | ||
| + | contents="R b1 a3 E A:a2 B:b2" | ||
| + | /> | ||
| + | If Blue intrudes at A, Red may defend the bridge at B (or [[tenuki|play elsewhere]]). If Blue intrudes at B, Red may defend the bridge at A. Either way, Blue gains a bit of [[territory]] on one side of the bridge (but not the other). Blue is faced with the choice of which side of the bridge to intrude upon (if any). | ||
| + | |||
| + | === Ziggurat intrusion === | ||
| + | |||
| + | In the [[ziggurat]], there are 8 potential intrusion points A–H: | ||
| + | <hexboard size="3x4" | ||
| + | coords="none" | ||
| + | edges="bottom" | ||
| + | visible="area(c1,a3,d3,d1)" | ||
| + | contents="R c1 E A:d1 B:b2 C:c2 D:d2 E:a3 F:b3 G:c3 H:d3" | ||
| + | /> | ||
| + | |||
| + | == Good intrusion == | ||
| + | |||
| + | Which of several possible intrusions to play is a difficult question that depends on what else is going on on the board and what the intruding player would like to achieve. But generally speaking, it is usually better to intrude along the outside of a template, rather than in its center. A typical situation is the following: | ||
| + | <hexboard size="4x6" | ||
| + | coords="none" | ||
| + | edges="bottom right" | ||
| + | contents="B a3 R c2 S area(c2,a4,d4,d2) E A:d2 B:b3 C:c3 D:d3 E:a4 F:b4 G:c4 H:d4" | ||
| + | /> | ||
| + | Suppose Blue wishes to intrude into Red's [[ziggurat]]. If Blue intrudes at F (near the center of the template), Red reconnects at D. By further intruding into Red's bridge, Blue gets at most a 2nd row [[ladder escape]] along the right edge: | ||
| + | <hexboard size="4x6" | ||
| + | coords="none" | ||
| + | edges="bottom right" | ||
| + | contents="B a3 R c2 S area(c2,a4,d4,d2) B 1:b4 R 2:d3 B 3:d2 R 4:c3" | ||
| + | /> | ||
| + | On the other hand, if Blue intrudes at D (near the edge of the template), Red reconnects at F, and Blue gets a 3rd row ladder escape: | ||
| + | <hexboard size="4x6" | ||
| + | coords="none" | ||
| + | edges="bottom right" | ||
| + | contents="B a3 R c2 S area(c2,a4,d4,d2) E D:d3 F:b4 B 1:d3 R 2:b4" | ||
| + | /> | ||
| + | However, not all intrusions along the template's outsides are good in all circumstances. For example, if Blue tries to intrude at H, Red may respond at A, forming [[edge template III2a]] and leaving Blue with only a 2nd row escape: | ||
| + | <hexboard size="4x6" | ||
| + | coords="none" | ||
| + | edges="bottom right" | ||
| + | contents="B a3 R c2 S area(c2,a4,d4,d2) B 1:d4 R 2:d2" | ||
| + | /> | ||
| + | Similarly, if Blue intrudes at A, Red may reconnect at D, forming [[edge template III2e]] and again leaving Blue with only a 2nd row escape: | ||
| + | <hexboard size="4x6" | ||
| + | coords="none" | ||
| + | edges="bottom right" | ||
| + | contents="B a3 R c2 S area(c2,a4,d4,d2) B 1:d2 R 2:d3" | ||
| + | /> | ||
| + | If Blue intrudes at C, the situation is even worse for Blue: Red can reconnect at A, leaving Blue with nothing useful at all: | ||
| + | <hexboard size="4x6" | ||
| + | coords="none" | ||
| + | edges="bottom right" | ||
| + | contents="B a3 R c2 S area(c2,a4,d4,d2) B 1:c3 R 2:d2" | ||
| + | /> | ||
| + | Thus, Blue must carefully choose the best intrusion for the given situation. | ||
| + | |||
| + | == Bad intrusion == | ||
| + | |||
| + | Some intrusions are actually counterproductive. One example of this is intruding on the wrong side of a [[bolstered template|bolstered bridge]], or more generally, of a [[bolstered template]]. For example, consider this situation. | ||
| + | <hexboard size="3x2" | ||
| + | coords="none" | ||
| + | edges="none" | ||
| + | visible="area(b1,a1,a3,b2)" | ||
| + | contents="R a1 b1 a3 E A:a2 B:b2" | ||
| + | /> | ||
| + | If Blue intrudes at A, Red's response at B actually [[dead cell|kills]] Blue's stone. Therefore, such an intrusion does not help Blue at all, but helps Red instead. See the article on [[bolstered templates]] for more details. | ||
| + | |||
| + | == Invalid intrusion == | ||
| + | |||
| + | When intruding into one of the opponent's templates or virtual connections, a player must be careful to take into account all of the possible ways in which the opponent is connected. For example, consider the following situation. | ||
| + | <hexboard size="3x5" | ||
| + | coords="none" | ||
| + | edges="bottom" | ||
| + | visible="area(c1,a3,e3,e1)" | ||
| + | contents="R d1 E A:c3" | ||
| + | /> | ||
| + | If Blue tries to intrude at A, Blue does not even threaten to disconnect Red, because in addition to two different ziggurats, Red is also connected by [[edge template III1b]]:<hexboard size="3x5" | ||
| + | coords="none" | ||
| + | edges="bottom" | ||
| + | visible="area(c1,a3,e3,e1)" | ||
| + | contents="R d1 S area(c1,a3,e3,e1)-c3 E A:c3" | ||
| + | /> | ||
| + | An intrusion, by definition, must threaten to disconnect Red. Therefore, playing at A is not be a valid intrusion at all. Instead, it is likely a [[irrelevant move|wasted move]]. | ||
| + | |||
| + | One situation where an invalid intrusion can be beneficial is [[losing play#Feinting|feinting]]. | ||
| + | |||
| + | == Intrusion vs. blocking == | ||
| + | |||
| + | An intrusion is not the same thing as [[blocking]]. By definition, an intrusion is into an area where the opponent is already [[virtual connection|virtually connected]]; therefore, the opponent can always re-establish the connection. By contrast, the goal of a [[blocking|blocking move]] is to disconnect the opponent. As mentioned above, intrusions are often best played on the outside of the connection, whereas blocking moves are best played near the inside. Thus, attempting a blocking move when the opponent already has a virtual connection is often catastrophic; conversely, attempting an intrusion when the opponent actually could have been blocked is also catastrophic. For this reason, it is very important to be able to [[reading|read]] whether the opponent is already connected or not. The corresponding [[proverbs|proverb]] is: "''Don't defend the indefensible.''" | ||
| + | |||
| + | == See also == | ||
| + | |||
| + | * Some intrusions are [[peeps]]. | ||
Revision as of 06:35, 1 October 2023
An intrusion is a move that threatens to disconnect a virtual connection of the opponent. The most common kind of intrusion is a template intrusion, which is a move inside the carrier of one of the opponent's templates.
By definition, a template or a virtual connection can always be defended, and therefore, intruding into a template does not actually disconnect the opponent (unless the opponent declines to defend the template). Nevertheless, a well-played intrusion can be to the benefit of the intruding player. For example, the intruding player may gain a bit of territory or a ladder escape.
Choosing which one of several possible intrusions is the most advantageous is one of the most difficult skills in Hex.
Contents
Examples
Bridge intrusion
The most basic template is the bridge. It has two potential intrusions: at A or at B.
If Blue intrudes at A, Red may defend the bridge at B (or play elsewhere). If Blue intrudes at B, Red may defend the bridge at A. Either way, Blue gains a bit of territory on one side of the bridge (but not the other). Blue is faced with the choice of which side of the bridge to intrude upon (if any).
Ziggurat intrusion
In the ziggurat, there are 8 potential intrusion points A–H:
Good intrusion
Which of several possible intrusions to play is a difficult question that depends on what else is going on on the board and what the intruding player would like to achieve. But generally speaking, it is usually better to intrude along the outside of a template, rather than in its center. A typical situation is the following:
Suppose Blue wishes to intrude into Red's ziggurat. If Blue intrudes at F (near the center of the template), Red reconnects at D. By further intruding into Red's bridge, Blue gets at most a 2nd row ladder escape along the right edge:
On the other hand, if Blue intrudes at D (near the edge of the template), Red reconnects at F, and Blue gets a 3rd row ladder escape:
However, not all intrusions along the template's outsides are good in all circumstances. For example, if Blue tries to intrude at H, Red may respond at A, forming edge template III2a and leaving Blue with only a 2nd row escape:
Similarly, if Blue intrudes at A, Red may reconnect at D, forming edge template III2e and again leaving Blue with only a 2nd row escape:
If Blue intrudes at C, the situation is even worse for Blue: Red can reconnect at A, leaving Blue with nothing useful at all:
Thus, Blue must carefully choose the best intrusion for the given situation.
Bad intrusion
Some intrusions are actually counterproductive. One example of this is intruding on the wrong side of a bolstered bridge, or more generally, of a bolstered template. For example, consider this situation.
If Blue intrudes at A, Red's response at B actually kills Blue's stone. Therefore, such an intrusion does not help Blue at all, but helps Red instead. See the article on bolstered templates for more details.
Invalid intrusion
When intruding into one of the opponent's templates or virtual connections, a player must be careful to take into account all of the possible ways in which the opponent is connected. For example, consider the following situation.
If Blue tries to intrude at A, Blue does not even threaten to disconnect Red, because in addition to two different ziggurats, Red is also connected by edge template III1b:An intrusion, by definition, must threaten to disconnect Red. Therefore, playing at A is not be a valid intrusion at all. Instead, it is likely a wasted move.
One situation where an invalid intrusion can be beneficial is feinting.
Intrusion vs. blocking
An intrusion is not the same thing as blocking. By definition, an intrusion is into an area where the opponent is already virtually connected; therefore, the opponent can always re-establish the connection. By contrast, the goal of a blocking move is to disconnect the opponent. As mentioned above, intrusions are often best played on the outside of the connection, whereas blocking moves are best played near the inside. Thus, attempting a blocking move when the opponent already has a virtual connection is often catastrophic; conversely, attempting an intrusion when the opponent actually could have been blocked is also catastrophic. For this reason, it is very important to be able to read whether the opponent is already connected or not. The corresponding proverb is: "Don't defend the indefensible."
See also
- Some intrusions are peeps.
