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BeginnerExercise4

 

Beginner Exercise 4 Solution
  Difficulty: Beginner  

KarlKnechtel, filling in a solution.

[Diagram]
Diag.: Solution.

Quickest explanation (not at all useful to those for whom this was challenging): "1 is tesuji. 2 and 3 are miai for the kill."

How I'd explain it to someone a bit below my level: "The throw-in at 1 threatens to capture the marked stone, and Black cannot connect because he is in oiotoshi - Black 2 at 3 is answered by the capture with White 3 at 2. So Black captures, making one eye; but White 3 destroys the other eye."

SAS: This isn't oiotoshi, at least not as I understand the term. Black cannot connect because of shortage of liberties (damezumari). Oiotoshi is a specific method of capture involving shortage of liberties. (The Go Player's Almanac defines it as "capturing by creating a shortage of liberties through a series of sacrifices".)

In easier terms: Black needs two eyes to live. There is already one virtually at a, so White must prevent the centre space from becoming an eye. The sacrifice changes the shape of that space, achieving the goal.

This problem is small enough that we can consider all the alternatives:


[Diagram]
Diag.: Reference.

Playing elsewhere is answered by Black either at a or b. (b claims an extra point of territory, at the expense of a ko threat for White. The play at a is safe from that, as I'd originally thought, but I managed to confuse myself somehow. Thanks SAS. :) Anyway - see Points Or Ko Threats Discussion for more information about that sort of tradeoff. ) So clearly white has to do something.

(Incidentally, the eye around a is an example of what I call a two-space elbow. Not that it really matters.)

unkx80: I think that b is better than a in the context of this question, for two reasons: (1) It claims an extra point of territory, (2) It creates a cutting point. The group in Points Or Ko Threats Discussion is different in the sense that either of the two points there has equal value except for ko threats, so the one giving less ko threats might be better.

[Diagram]
Diag.: Failure.

One try is to threaten the existing eye; but the capture solves all of Black's problems. (Connecting at a would be very bad for Black; White doesn't even have to capture.) This is also a throw-in, but it's the wrong one and doesn't help.


[Diagram]
Diag.: Failure.

Moving to make the other eye false looks good at first, because Black is in atari to start off with. But all Black has to do is connect. Again, the two eyes are solid.


[Diagram]
Diag.: Good for white?

I'm new to Go but enjoying learning about it a lot. The above confuses me a little. Could someone explain why the sequence 1, 2, 3 isn't good for White? Is it that White would really have played 2 at 3 resulting in a ko? --DaveFinlay

Answer: White 3 is a forbidden move now. It is placing a stone at a point without any liberties while not capturing any stones.

Thanks. I don't know what I was thinking. DaveFinlay





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