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Need help with 'Basics: Step-by-step Lesson 04 C - problem 1061_00d.sgf'

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2016-05-12 12:06
Satorian Hello everyone,

I need help with the problem given in the title.

I can't figure out how the potential eye shape in the middle is supposed to be a half eye. To me it seems that even if black moves first, white can always invalidate the shape.

I'm stuck here and my mind is blocked from seeing a solution here.

Help would be much appreciated!


2016-05-12 14:39
Darrell Malick Hi Michael,

Yes, it is potentially confusing. Remember that 2 half eyes is a dead group. 2 half eyes is a situation where if Black can move twice in a row, Black gets 2 eyes.

Given that hint, you should see that if Black gets two moves in a row and fills the two shoulders on the center eye, Black has 2 eyes.

Make sense?

2016-06-14 23:43
geroldn Hi Darrell,

I don't agree with your approach. A half eye can be made an eye in sente. That means that if you have two half eyes one can always be made an eye, also in gote. That is not the case here.

Suppose the left false eye would be an eye by adding two black stones on D9 and D11. Then one eye and two half eyes would live. Still the group is dead in gote because white K9 invalidates both so-called half eyes at once.

Calling the middle 'eye' a half eye is wrong in my opinion. There is one half eye and two false eyes.

Please let me know if I am mistaken.


2016-06-15 16:06
Guo Juan Fixed. Thanks.

2016-06-15 19:05
Darrell Malick Looks like Guo Juan agrees with you. :) However: A half eye is an eye that can be made in *gote*. Probably that's what you meant, but just making sure. Thanks for the post and the persistence!

2016-06-16 20:58
geroldn With 'in sente' I meant it being your turn. This is probably not a correct way to use the term. A player 'has sente' means it is his turn (Sensei's Libarary). This is what I meant.

2016-06-18 08:06
Darrell Malick Ok, I understand.

Yes, as you say: "I can do something in sente" or "with sente" it means you can do it and *keep* sente.

"Having sente" is as you describe - you get to decide where to play next.

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