| * | Two eyes (the smallest way to live) | |
| As we saw, the black group in Dia. 1 is alive. It's the smallest living shape that can never be captured. It has two breathing spaces that are completely blocked off by black stones. The territory inside the group is clearly separated into two spaces, so they are called two eyes. |
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| Dia. 1 | ||
| Dia. 2. When Black has two eyes, White can't invade with the marked stone. Even if he invades, Black still has the breathing space marked with a yellow x, so White can't capture. You can only invade inside Black's territory when your stone has one or more breathing spaces of its own; if the invading stone has no breathing spaces, you can invade only when your move fills the last breathing space of the opponent (that is, you capture Black). |
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| Dia. 2 | ||
| * | A dangerous situation | |
| Dia. 3. This black territory has three points inside it, so you might think that the group is alive. However, this group is in acute danger. If Black plays a stone in the centre of his territory, he gets two separate eyes and is completely alive, but if White plays a stone on the centre point, Black is reduced to one eye, so he dies. |
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| Dia. 3 | ||
| Dia. 4. When White plays the marked stone, Black can no longer divide his territory into two, so he dies. | ||
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| Dia. 4 | ||
| In short, in order to live, you need to be able to divide your territory into two spaces when the opponent invades. | ||
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| Only one space is dead. | Two spaces make you alive. | |