False Eyes

 Take a look at this white group. It looks as if it has two eyes, doesn't it? But there's a big problem: the marked stone is in atari. If Black captures the stone, the white group has only one eye. But if White saves the stone, it still has only one eye! So this white group is already dead. There's no way to save it from being captured. Something that looks like an eye but is going to get filled in eventually is called a false eye. To be alive you need two real eyes. False eyes don't help. Here's another shape that makes a false eye. The three marked stones in an L shape are in atari, so the space next to them isn't a true eye. The whole white group is dead! Here's one last shape to know. The 5 white stones are like a letter U turned on its side. They are in atari too, so they make a false eye. This white group is dead too. For an eye to be false, the stones next to it don't need to be in atari right now, so long as they can be put in atari eventually. The marked stones here aren't in atari yet, but they would be once the points marked x are filled in. So the eye on the left is a false one, and the white stones are already dead!

 Remember!

 If some stones can be put into atari sooner or later, an empty point next to them doesn't count as an eye.

 Challenge! Find the vital point!

In each case, find the point where Black would play to make a real eye, or White would play to make a false eye.

 Super-Challenge!

 How many of the black stones can you change to white ones without making a false eye?

 Take a break!

When you're ready for more, click where you want to go.

 1 November 2003