Ferran wrote:
I've been having a bit of a weird week, schedule-wise, so I've tried to use the time to restart my DDK tsumego. On one of the books I've found several quirky solutions, for my understanding. Now, I *know* I see some tsumego differently, that my answer "works" but is not always the preferred option. Sometimes I understand why, sometimes I don't. In this case, I *think* some of the answers are wrong.
My 2¢.
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The book claims this is a seki, 'a' being the unplayable point (there must be a name for that). I see it unconditionally alive. What am I missing?
The "unplayable point" is called a shared dame or an internal dame.
Seki is unconditionally alive.
(Note: That is the traditional way of using the term unconditionally alive. In some contexts people use the term to mean that a group is alive even if its owner always passes. But in problems it means that a group is alive with correct play against any attack, except possibly in a ko fight.)
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This one shows something that always bugs me of these things. White's level is alternatively about par with Black's or significantly lower.
I agree that that is a ridiculous question.
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I don't understand this kind of solution. 4 is one move away. If Black can see seven moves away, surely White can see a single one? Then, 4 at a, 5 captures at the marked stone. Should Black atari at b, then 6 at, well, 6 has already connected and, can play at 7 for a connection outside. Capturing a becomes gote. The specific example aside, there are many problems where Black can't be greedy, but White is nothing but. There's not "damage control", of sorts. And I'm not sure what part is me being DDK, what part is just the way things are done...
You can't say that you have solved a problem unless you have an answer for every reply of the opponent. The sequence shown in the diagram is necessary to show that
solves the problem. So is the sequence where White plays 
at 3, but that obviously gives up.Unfortunately, the book asks not for Black to capture four stones, but how strong White is. Apparently it does not say that Black is to play and capture some White stones. So what is a solution?
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Another example of the same kind...
Why would white ever play 2? It's self-atari, it makes no sense. It's one move away. 2 at 3, 3 at 2, 4 at a. Or even 2 at a, then pick whichever's left after black plays 3 at either 2 or 3. I don't know, but the point is that we wouldn't allow Black, in an exercise, to self-atari at the very first move, would we? As I understood tsumego, both sides are supposed to try the better move available. I understand a book for DDK can't ask for the moon, but this is looking a single move ahead... So, what am I missing? This is not the only book I've had the feeling with, it's just that the first example really puzzles me.
Why would white ever play 2? It's self-atari, it makes no sense. It's one move away. 2 at 3, 3 at 2, 4 at a. Or even 2 at a, then pick whichever's left after black plays 3 at either 2 or 3. I don't know, but the point is that we wouldn't allow Black, in an exercise, to self-atari at the very first move, would we? As I understood tsumego, both sides are supposed to try the better move available. I understand a book for DDK can't ask for the moon, but this is looking a single move ahead... So, what am I missing? This is not the only book I've had the feeling with, it's just that the first example really puzzles me.
is not self atari. 
is atari. 
at 1 would be self-atari, AKA connect-and-die.Again, the sequence given is necessary to show that
solves the problem. Also, gives up no points locally. Here is the result of that sequence of play.And here is the result when
simply connects.In the second diagram Black has captured 2 White stones in a snapback, for 5 pts. of territory. In the first diagram Black has captured 3 White stones and White has captured 1 Black stone. Adding the 3 pts. of territory on the board gives Black a net local score of 5 pts. (The difference is that White has lost a ko threat, but the local score is the same.
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As I understood tsumego, both sides are supposed to try the better move available.
Only the solver is supposed to play correctly. The opponent can, and ideally should, try anything. It is up to the solver to counter whatever the opponent may throw at him.
Edit: OC, in a failure diagram, where the solver makes a mistake, the opponent is supposed to play correctly after the mistake, to show that the solver's play fails.
is unconditionally alive" = an implicit assumption that 
