Life In 19x19

Tsumego pro is a very nice app for android tablets and provides daily exercises. Today it bluntly declared my solution to the first hard problem as wrong. I am not sure tsumegopro is correct.
Thx for your advice.

Click Here To Show Diagram Code

[go]$$Bc
$$ +-------------------
$$ | . . . . . . . . .
$$ | . . . . . . . . .
$$ | . . O . . . . . .
$$ | . . . O . O . . .
$$ | . O O X O . . . .
$$ | O X X X O O . . .
$$ | . O O X X X O . .
$$ | . . . . . X O . .
$$ | . . X X X X O . .
$$ | . . X O X O O . .
$$ | . X O O O . . . .
$$ | . O . . . . . . .
$$ | . . O . . . . . .
$$ | . . . . . . . . .[/go]

black to play ...

Here my solution and tsumego's solution

EDIT: D'oh. deleting my answer, didn't notice the atari on the upper side....why I'm still on the beginner problems...

Bonobo showed me how to become famous by answering your own questions. So here I go.

Click Here To Show Diagram Code

[go]$$Bc
$$ +-------------------
$$ | . . . . . . . . .
$$ | . . . . . . . . .
$$ | . . O . . . . . .
$$ | . . . O . O . . .
$$ | . O O X O . . . .
$$ | O X X X O O . . .
$$ | 2 O O X X X O . .
$$ | a 1 4 5 . X O . .
$$ | 3 . X X X X O . .
$$ | . b X O X O O . .
$$ | 6 X O O O . . . .
$$ | . O . . . . . . .
$$ | . . O . . . . . .
$$ | . . . . . . . . .
$$ | . . . . . . . . .[/go]

at a or at be that is the question.

1. and both proof that the combination solves the problem.
2. Both a and b proof that equally well. In that sense there is no best
3. the app shouldn't disapprove of my solution ( at a ).
3. w won't answer until the endgame or as threats in a ko fight.
4. If in a ko fight W eventually threatens at B will answer at a because the penalty of not answering it is more severe than after b.
5. The proverb sente first gote later is a good guide in situations like this.
6. Only if you can attack W's south wing playing at b might be better.

cyclops wrote:Bonobo showed me how to become famous by answering your own questions. So here I go.

$$Bc
$$ +-------------------
$$ | . . . . . . . . .
$$ | . . . . . . . . .
$$ | . . O . . . . . .
$$ | . . . O . O . . .
$$ | c O O X O . . . .
$$ | O X X X O O . . .
$$ | 2 O O X X X O . .
$$ | a 1 4 5 . X O . .
$$ | 3 . X X X X O . .
$$ | . b X O X O O . .
$$ | 6 X O O O . . . .
$$ | . O . . . . . . .
$$ | . . O . . . . . .
$$ | . . . . . . . . .
$$ | . . . . . . . . .

Click Here To Show Diagram Code

[go]$$Bc
$$ +-------------------
$$ | . . . . . . . . .
$$ | . . . . . . . . .
$$ | . . O . . . . . .
$$ | . . . O . O . . .
$$ | c O O X O . . . .
$$ | O X X X O O . . .
$$ | 2 O O X X X O . .
$$ | a 1 4 5 . X O . .
$$ | 3 . X X X X O . .
$$ | . b X O X O O . .
$$ | 6 X O O O . . . .
$$ | . O . . . . . . .
$$ | . . O . . . . . .
$$ | . . . . . . . . .
$$ | . . . . . . . . .[/go]

at a or at be that is the question.

"a" and "c" are miai, forming a two-way ko threat. Since White's threat is much larger than Black's, it can hardly be wrong for Black to play at "a" to eliminate White's threat.

Besides, and are for illustrative purposes. In a real game White would play first.

Bill Spight wrote: Besides, and are for illustrative purposes. In a real game White would play first.

So next diagram shows the normal evolution.

Click Here To Show Diagram Code

[go]$$Bc :b11:@d
$$ +-----------------
$$ | . . . . . . . .
$$ | . . . . . . . .
$$ | . . O . . . . .
$$ | . . . O . O . .
$$ | 8 O O X O . . .
$$ | O X X X O O . .
$$ | 2 O O X X X O .
$$ | 9 1 6 7 . X O .
$$ | 3 . X X X X O .
$$ | d 5 X O X O O .
$$ | 4 X O O O . . .
$$ | 0 O . . . . . .
$$ | . . O . . . . .
$$ | . . . . . . . .[/go]

In hindsight my question was not of that much interest.

cyclops wrote:

Bill Spight wrote: Besides, and are for illustrative purposes. In a real game White would play first.

So next diagram shows the normal evolution.

$$Bc :b11:@d
$$ +-----------------
$$ | . . . . . . . .
$$ | . . . . . . . .
$$ | . . O . . . . .
$$ | . . . O . O . .
$$ | 8 O O X O . . .
$$ | O X X X O O . .
$$ | 2 O O X X X O .
$$ | 9 1 6 7 . X O .
$$ | 3 . X X X X O .
$$ | d 5 X O X O O .
$$ | 4 X O O O . . .
$$ | 0 O . . . . . .
$$ | . . O . . . . .
$$ | . . . . . . . .

Click Here To Show Diagram Code

[go]$$Bc :b11:@d
$$ +-----------------
$$ | . . . . . . . .
$$ | . . . . . . . .
$$ | . . O . . . . .
$$ | . . . O . O . .
$$ | 8 O O X O . . .
$$ | O X X X O O . .
$$ | 2 O O X X X O .
$$ | 9 1 6 7 . X O .
$$ | 3 . X X X X O .
$$ | d 5 X O X O O .
$$ | 4 X O O O . . .
$$ | 0 O . . . . . .
$$ | . . O . . . . .
$$ | . . . . . . . .[/go]

In hindsight my question was not of that much interest.

Well, in a real game, White would probably play elsewhere after , saving , , and as potential ko threats. But in a problem it is important to have White play them. is important, because Black could misplay . and are important to show that White cannot take away the eye on the second line because of damezumari.

But it is silly to criticize your in the problem line, and, to judge from complaints here, that kind of thing is not uncommon with interactive problem software. I think that that is an important issue to raise.

Thx, Bill, for your clarifications.
For completeness I added my refutation for another .

Click Here To Show Diagram Code

[go]$$Bc :w8: @a-> :b9: @e
$$ +-----------------
$$ | . . . . . . . .
$$ | . . . . . . . .
$$ | . . O . . . . .
$$ | . . . O . O . .
$$ | . O O X O . . .
$$ | O X X X O O . .
$$ | 7 O O X X X O .
$$ | a 1 e . . X O .
$$ | 3 5 X X X X O .
$$ | 4 2 X O X O O .
$$ | 6 . O O O . . .
$$ | . O . . . . . .
$$ | . . O . . . . .
$$ | . . . . . . . .[/go]