Senket — A More Costly Invasion

 

 

Red pays the price for not protecting the corner.

Red pays the price for not protecting the corner.

Here Red has a bit more to lose, and he’s going to. Blue starts off with the post at 1. As in the previous example, there is no way for Red to capture Blue; he can only perform damage control. Red’s post and fence at 2 are designed to minimize Blue’s incursion. Blue 3 locks down Blue’s territory; on his next move he’ll either play at 5 or A, and Red can only block one of them. 

 

However, it doesn’t make sense for Red to play directly on either of these spots. Playing at 5 would just invite Blue to play at A, taking an additional 2 units and a prisoner. Playing at A is better, but turns this exchange into Sente for Blue, who won’t need to play 7. Instead, Red 4 is best. Blue has to play at 5 to make territory. Otherwise Red would play at 5, capturing Blue.

At this point Red has a choice: 6 or 7. Both make territory, and whichever one Red chooses, Blue can then block the other with a single move. 7 is worth 6 units. 6 is worth 7 units, so 6 is better.

After that, Blue can play 7 to block Red from 6 units. Of course, if there is another play elsewhere that is bigger, Blue can ignore 7; he has territory and is safe. But assume Blue does play 7. What was this worth?

Originally, Red had 20 units. At the end he has 7 left, and Blue has picked up 2. So Blue picked up a total of 15 units in Gote, a very nice profit. In addition, Blue has the ability to pick up another unit in the corner, which could come in handy later in the game.

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