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TsumegoFromGames7

 

TFG7 Solution
    Keywords: Problem

[Diagram]
Diag.: Solution

Jonathan Cano White 1 threatens to capture the marked black stones. If white captures these she has a second eye and is alive so black defends at 2 (he could also defend by playing at a).

Because of 1, white 3 is now sente. White 5 is also sente...

After 7 c and d are miai.

Note: the exact order of 1, 3 and 5 is not important. white could play: 5-1-3 or 1-5-3.


[Diagram]
Diag.: Solution, continued

For example: if black 8, white 9. In "All about Life and Death" volume one by Cho Chikun, the position of the marked white stones appears as "pattern 6" and is shown to be alive.


[Diagram]
Diag.: All About Life and Death, Pattern 6

If you know this pattern is alive (i.e. if black plays first, like at a white can still live) then the solution to this problem is not so hard.

I hope you enjoyed this problem.



Dieter found it in 5 seconds, but omitted 5 in the solution diagram. It is not needed for life but as KikashiBeforeLiving? it is OK I guess. 3 (in the first solution diagram) is the one that matters and is made possible by 1. Level of this problem is difficult to determine. I know 2 Dans who don't know about the L-group and 9 kyus who do.

Jonathan Cano: Here is a diagram showing Deiter's amended solution:

[Diagram]
Diag.: Solution

c and d are still miai. It is generally better to avoid unnecessary moves in sequences like this. Playing 5 in the previous solution (white e, black f) squanders a kikashi that would serve as a nice threat should a ko arise. Thank you Dieter.



[Diagram]
Diag.: Other Solution

jesusin(3K): I had an idea similar to Dieter's. In the solution I would omit 1. White 3 is sente even if 1-2 have not been exchanged. In the diagram "Other Solution" below W1 makes 'a' and 'b' miai.

Jonathan Cano: Cool! Occam's razor cuts away yet another unnecessary move! If black responds to 1 at b this looks like a territorial loss for white compared to white playing at b first.

In the actual game I did not realize that "just 1" would work so I didn't have the chance to contrast its merits with the original solution.



BillSpight: Hi, Jonathan! Good to see you again. :-)

Aside from the question of timing, there are a couple of problems with the proposed solution.

[Diagram]
Diag.: Miai? Not!

First: 8 and 9 are miai-ish, but 8 is more equal. ;-) Black should play there. In fact, B 8 is urgent, as explained below.

Jonathan Cano: OK OK, for an endgame bean counter like yourself 8 and 9 may not be miai but for a poor sod (like me) just trying to determine life & death status calling 8 & 9 miai for L&D purposes is good enough.

Of course, once status has been determined (white can live), then we should get into the matter of how to play best (as you have).


[Diagram]
Diag.: Get it while you can

BillSpight: Second: Previously, after B 6, White should take kikashi with W 7 - B 8 before playing W 9.

Why?


[Diagram]
Diag.: Double sente

If White omits B 5 before playing B 1, Black will play B 2 - W 3. Later, if White plays W 5 Black does not have to play at a but can capture White's stone with B 6. After W 1, B 2 and W 5 are double sente. After B 2 - W 3, W b is better than W 5. That mitigate's White's loss from not playing W 5 first. It comes to only 1/6 of a point, but hey!


Jonathan Cano: Bill, which solution do you think is best? I know this can vary according to circumstance so please describe a few scenarios in which different sequences are best. For example, Get it while you can seems to maximize white's local score (is this the best variation for this purpose) but is this also the best solution if white is concerned that she may have to fight a ko later?


[Diagram]
Diag.: Bean Counter's Solution

Bill: ;-).

Well, really: White's alive, and White's threat to take a couple of stones is nothing compared to Black's threat to kill. :-)

Black now has an 8 point sente.

Jonathan Cano: to put it in plain english, since the threat to capture two black stones (with white a) is so small (5 points? -- how do you get 8 points sente above?),

(Bill: Add the 3 marked points in the corner.)

it is very likely black should switch elsewhere.


[Diagram]
Diag.: Black Sente

Bill: B a is the same size as B 1, but leaves a ko threat behind (in most variations) at 1. If White omits the kikashi, W 2 - B 3, before W 4, Black can later play sente at b, threatening to kill at c. Omitting the kikashi costs more than 1 point.

White now has a 3 point sente.


[Diagram]
Diag.: White Sente

Now if W a, B b. c is a ko threat.


[Diagram]
Diag.: Death Threat

B 1 is the final threat to kill, worth between 1 1/3 and 1 1/4 points. Later a and b are 1 point plays.

In this sequence each player preserves her aji as long as possible.

Jonathan Cano: Thanks Bill.





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