Tsumego From Games 7 / Solution

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, the points 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.

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.

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.

Solution  

The points 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.

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 White 1 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.

Miai? Not!  

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

Get it while you can  

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

Why?

Double sente  

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

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 play.

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 three marked points in the corner.)

it is very likely Black should switch elsewhere.

Black sente  

Bill: Black a is the same size as Black 1, but leaves a ko threat behind (in most variations) at 1. If White omits the kikashi, White 2 - Black 3, before White 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 three-point sente play.

White sente  

Now if White a, Black b. Here c is a ko threat.

Death threat  

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

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

Jonathan Cano: Thanks Bill.