This 'n' that

Bill Spight · Post by **Bill Spight** » Wed Sep 20, 2017 7:37 pm

Apparently some people have altered the game record to make it come out in accordance with the score. So maybe I'm re-treading well trodden ground, but I thought that I would give it a try, too.

Click Here To Show Diagram Code: [go]$$Wcm36 Mistakes $$ --------------------------------------- $$ | . O . . . . . . O O . X X . X X X O . | $$ | X O 7 . X O O O X X X . . X X O O O . | $$ | 6 X O O O O X O O O O X X X X X X O . | $$ | . X X X O . X X 1 , O O O X X O O . . | $$ | . . . . X X . X O O . X X X O O . O . | $$ | . . . . X O O X O X X . X O O X O . . | $$ | . . X . . X O X X X O X X X X X O O . | $$ | . . . . . X O O . X O O O O X . X O O | $$ | . . . . . X O O . O O X . 5 X . X X O | $$ | X X . , . X O X O , O X X X . , . . X | $$ | O X X X . . X X a O X X O O X X O X . | $$ | O O X O X X O X . O O O X O O O X X X | $$ | . O O O O X O X O O X X X X O . O O O | $$ | . . O X O O O X X O X X O O O O O . O | $$ | . . O X . X . O X O O X X . . X X O O | $$ | . . . O X X O . O , 4 . . O O X O X X | $$ | . . O . O X . O . O O X X X X X O X . | $$ | . . . . O X . . O X X X . . . . O X . | $$ | . . . . . . . . 3 O 2 . . . . . . . . | $$ ---------------------------------------[/go]

Backing the game up to move 236, we can see that Black 241 and White 242 should be at "a". But they look like a neutral point and a protective play, simple formalities that could easily have ended play. It is certainly plausible that someone had already played at "a" before they were played. But White 236 is an error. It gains only ½ pt., while there is a reverse sente that gains 1 pt., at 237.

Click Here To Show Diagram Code: [go]$$Wcm36 Correct play, but . . . . $$ --------------------------------------- $$ | . O . . . . . . O O . X X . X X X O . | $$ | X O 9 . X O O O X X X . . X X O O O . | $$ | 8 X O O O O X O O O O X X X X X X O . | $$ | . X X X O . X X 5 , O O O X X O O . . | $$ | . . . . X X . X O O . X X X O O . O . | $$ | . . . . X O O X O X X . X O O X O . . | $$ | . . X . . X O X X X O X X X X X O O . | $$ | . . . . . X O O . X O O O O X . X O O | $$ | . . . . . X O O . O O X . 7 X . X X O | $$ | X X . , . X O X O , O X X X . , . . X | $$ | O X X X . . X X 6 O X X O O X X O X . | $$ | O O X O X X O X . O O O X O O O X X X | $$ | . O O O O X O X O O X X X X O . O O O | $$ | . . O X O O O X X O X X O O O O O . O | $$ | . . O X . X . O X O O X X . . X X O O | $$ | . . . O X X O . O , 4 . . O O X O X X | $$ | . . O . O X . O . O O X X X X X O X . | $$ | . . . . O X . . O X X X . . . . O X . | $$ | . . . . . . . . 3 O 1 2 . . . . . . . | $$ ---------------------------------------[/go]

If White plays correctly, then White 238 is the last effective play, since the plays that gain ½ pt. are miai. White and Black each get the same moves as in the game record, but Black also gets Black 241. White wins by 1 pt., but by 42 to 41 instead of 43 to 42. This is a possible reconstruction, but not one that makes a minimal change to the game record.

Click Here To Show Diagram Code: [go]$$Bcm29 Blunder $$ --------------------------------------- $$ | . O . . . . . . O O . X X . . 1 . a . | $$ | X O . . X O O O X X X . . X X O O 2 . | $$ | . X O O O O X O O O O X X X X X X O . | $$ | . X X X O . X X . , O O O X X O O . . | $$ | . . . . X X . X O O . X X X O O . O . | $$ | . . . . X O O X O X X . X O O X O . . | $$ | . . X . . X O X X X O X X X X X O O . | $$ | . . . . . X O O . X O O O O X . X O O | $$ | . . . . . X O O . O O X . . X . X X O | $$ | X X . , . X O X O , . . X X . , . . X | $$ | O X X X . . X X . O X X O O X X O X . | $$ | O O X O X X O X . O O O X O O O X X X | $$ | . O O O O X O X O O X X X X O . O O O | $$ | . . O X O O O X X O X X O O O O O . O | $$ | . . O X . X . O X O O X X . . X X O O | $$ | . . . O X X O . O , . . . O O X O X X | $$ | . . O . O X . O . O O X X X X X O X . | $$ | . . . . O X . . O X X X . . . . O X . | $$ | . . . . . . . . . O . . . . . . . . . | $$ ---------------------------------------[/go]

White 230 is a blunder. Would a Taoist immortal make that mistake? "a" is the obvious move. If we let White make the obvious move, everything falls into place.

Click Here To Show Diagram Code: [go]$$Bcm29 Possible game $$ --------------------------------------- $$ | . O . . . . . . O O . X X . . 1 . 2 . | $$ | X O . . X O O O X X X . . X X O O . . | $$ | . X O O O O X O O O O X X X X X X O . | $$ | . X X X O . X X 8 , O O O X X O O . . | $$ | . . . . X X . X O O . X X X O O . O . | $$ | . . . . X O O X O X X . X O O X O . . | $$ | . . X . . X O X X X O X X X X X O O . | $$ | . . . . . X O O . X O O O O X . X O O | $$ | . . . . . X O O . O O X . 0 X . X X O | $$ | X X . , . X O X O , 6 7 X X . , . . X | $$ | O X X X . . X X 9 O X X O O X X O X . | $$ | O O X O X X O X . O O O X O O O X X X | $$ | . O O O O X O X O O X X X X O . O O O | $$ | . . O X O O O X X O X X O O O O O . O | $$ | . . O X . X . O X O O X X . . X X O O | $$ | . . . O X X O . O , 5 . . O O X O X X | $$ | . . O . O X . O . O O X X X X X O X . | $$ | . . . . O X . . O X X X . . . . O X . | $$ | . . . . . . . . 4 O 3 . . . . . . . . | $$ ---------------------------------------[/go]

After White makes the correct play in the top right corner, :w30:

, Black 231 is sente. White 232 is the last effective play. The ½ pt. plays are miai, with each player getting the one in the published game record, and Black getting Black 237. After White 238 the rest are dame and protective plays. And this way the scores come out as in the published record.

OC, this is speculative, but it is also parsimonious, making minimal changes to the published record.

RobertJasiek · Post by **RobertJasiek** » Thu Sep 21, 2017 12:13 am

Bill, I cannot find quickly any positions of yours with the following aspects. Do you recall them or where to find them?

1) A basic endgame ko, some local non-ko not-only-dame endgames, possibly a few dames. There is no first move that is correct under area and territory scoring. I am not sure whether you found such positions. If not, maybe you can construct some?

2) Ca. 15 or 20 years ago, you found a position with different behaviour under area and territory scoring having only innocently looking shapes without any of the well-known exceptions related to sekis, kos or dames.

Bill Spight · Post by **Bill Spight** » Thu Sep 21, 2017 8:40 am

RobertJasiek wrote:Bill, I cannot find quickly any positions of yours with the following aspects. Do you recall them or where to find them?

1) A basic endgame ko, some local non-ko not-only-dame endgames, possibly a few dames. There is no first move that is correct under area and territory scoring. I am not sure whether you found such positions. If not, maybe you can construct some?

That may be something I posted on rec.games.go but found a flaw in a couple of years later. But it led to finding the button position, which has an average value of 1/2 by area scoring, and ought to have a score of 1/2 by territory scoring, but territory scores are integers. I believe that the button is on SL.

2) Ca. 15 or 20 years ago, you found a position with different behaviour under area and territory scoring having only innocently looking shapes without any of the well-known exceptions related to sekis, kos or dames.

That sounds like something that I found in discussion with Bernd Gramlich, again on rec.games.go.

So far, I have not identified anything in my records. I'll keep looking.

Bill Spight · Post by **Bill Spight** » Thu Sep 21, 2017 9:24 am

Cher Robert,

OC, there is the first problem in this thread.

See https://lifein19x19.com/forum/viewtopic ... 89#p194089

RobertJasiek · Post by **RobertJasiek** » Thu Sep 21, 2017 10:49 am

Bill Spight wrote:there is the first problem in this thread.

I did not mention it because territory scoring also allows the move that is correct under area scoring.

***

Let's hope Bernd Gramlich used lesfables then and not " " or "-" as his account name...

Bill Spight · Post by **Bill Spight** » Thu Sep 21, 2017 2:48 pm

RobertJasiek wrote:
Bill Spight wrote:there is the first problem in this thread.

I did not mention it because territory scoring also allows the move that is correct under area scoring.

Oh, I missed that.

0.75 - 0.5 = 0.5 - 0.75 + 0.5.

Bill Spight · Post by **Bill Spight** » Sun Sep 24, 2017 10:40 am

How not to teach the last play

Volume 5 in Sakata's classic Killer of Go series is The Tsume and Yose of Go. It combines tsumego with yose, a traditional practice of which I approve. The book devotes one page (three diagrams)

to the question of the last play. Here is the basic diagram.

Click Here To Show Diagram Code: [go]$$Bc Black to play, the rest of the board is jigo $$ --------------------------------------- $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . . . . . . . X O . . . . . . . O O | $$ | . X . . . . X . X O O O O X . . . O X | $$ | X X X X X X O X O X O X O O O O O X X | $$ | O X O O O X O X . X O X X . X O . . X | $$ | O X O X X X O X X X O O O O X O O O X | $$ | O O O O O O O O O O X X X X X X X X X | $$ | . . . . . . . . . . . . . . . . . . . |[/go]

Here, in brief, is what the book says. (The book was very probably ghost written, but Sakata signed off on it.)

Click Here To Show Diagram Code: [go]$$Bc Diagram 1 Black gets the last play $$ --------------------------------------- $$ | . . . . . . . . 3 1 2 . . . . . . . . | $$ | . . . . . . . . X O . . . . . . . O O | $$ | . X . . . . X . X O O O O X . . . O X | $$ | X X X X X X O X O X O X O O O O O X X | $$ | O X O O O X O X . X O X X 4 X O . 5 X | $$ | O X O X X X O X X X O O O O X O O O X | $$ | O O O O O O O O O O X X X X X X X X X | $$ | . . . . . . . . . . . . . . . . . . . |[/go]

is the last play. White wins by 1 pt.

Click Here To Show Diagram Code: [go]$$Bc Diagram 2 White gets the last play $$ --------------------------------------- $$ | . . . . . . . 3 2 4 . . . . . . . . . | $$ | . . . . . . . 5 X O . . . . . . . O O | $$ | . X . . . . X . X O O O O X . . . O X | $$ | X X X X X X O X O X O X O O O O O X X | $$ | O X O O O X O X . X O X X 1 X O . 6 X | $$ | O X O X X X O X X X O O O O X O O O X | $$ | O O O O O O O O O O X X X X X X X X X | $$ | . . . . . . . . . . . . . . . . . . . |[/go]

is the last play. Black wins by 1 pt.

Conclusion: Trying too hard to get the last play can be dangerous.

That's it! Nothing about the value of getting the last play, nothing about how to get it. Just a note of caution.

----

Well, today we know a good bit more about getting the last play. Berlekamp and Wolfe's Mathematical Go teaches us that, unless ko is a consideration, we can ignore plays that gain less than 1 pt. in considering the last play. That eliminates :b5:

in Diagram 1 and :w6:

in Diagram 2, each of which gains only ½ pt. The question of getting the last play, if it arises at all, is concerned with getting the last play at temperature 1 or higher. In this case it is White who gets the last play at temperature 3 in diagram 1 and Black who gets the last play at temperature 3 in diagram 2. So getting the last play matters in this case. You just have to understand the concept properly.

Bill Spight · Post by **Bill Spight** » Tue Sep 26, 2017 9:02 pm

Kano teaches about getting the last play

Kano does much better than Sakata. But Kano's Yose Dictionary is over 40 years old. The modern knowledge about getting the last play was yet to come. Kano discusses two positions, not just one. (Three examples if you count the miai example.

) Also, the positions have temperature 1, which is the place to start the study of getting the last play.

Click Here To Show Diagram Code: [go]$$Bc Black to play and get the last play $$ -------------------- $$ | . . . . . . . . . . $$ | . X . . . X X O . . $$ | . X . X . X O . O . $$ | . O X , X X O . . , $$ | . O . O O O O . . . $$ | . O . . . . . . . . $$ | . . . . . . . . . .[/go]

By the standard assumption, the surrounding territory belongs to White. There are three places to play, two hane-and-connects and the place around D-16. The hane-and-connects are miai, so this should be easy.

Click Here To Show Diagram Code: [go]$$Bc Black gets the last play $$ -------------------- $$ | . . . . . 5 4 6 . . $$ | . X . . . X X O . . $$ | 9 X . X . X O . O . $$ | 7 O X 3 X X O . . , $$ | 8 O 1 O O O O . . . $$ | . O 2 . . . . . . . $$ | . . . . . . . . . .[/go]

is sente, and then :b3:

takes the reverse sente. After that, the rest is miai, as advertised.

But here is Kano's first play diagram.

Click Here To Show Diagram Code: [go]$$Bc Failure $$ -------------------- $$ | . . . . . 9 8 0 . . $$ | . X . . . X X O . . $$ | 5 X 7 X . X O . O . $$ | 3 O X 6 X X O . . , $$ | 4 O 1 O O O O . . . $$ | . O 2 . . . . . . . $$ | . . . . . . . . . .[/go]

Good. White punishes Black's failure to play the reverse sente at 6. However, Kano does not blame :b3:

.

Click Here To Show Diagram Code: [go]$$Bc Black gets the last play (Kano) $$ -------------------- $$ | . . . . . . 3 1 2 . $$ | 5 X . . . X X O . . $$ | 4 X . X . X O . O . $$ | 6 O X 9 X X O . . , $$ | . O 7 O O O O . . . $$ | . O 8 . . . . . . . $$ | . . . . . . . . . .[/go]

is not a mistake, but what about :w4:

? It does not provide the stoutest resistance.

Click Here To Show Diagram Code: [go]$$Bc Stiffer resistance $$ -------------------- $$ | . . . . . . 3 1 2 . $$ | . X . . . X X O . . $$ | 7 X 9 X . X O . O . $$ | 5 O X 8 X X O . . , $$ | 6 O 4 O O O O . . . $$ | . O . . . . . . . . $$ | . . . . . . . . . .[/go]

It makes no difference in this case, but :w4:

is technically correct, as a play at 8 would be. :w4:

gives Black the chance to err by playing :b5:

at 8.

It is hard to fault Kano, given the state of knowledge in the early 1970s, but we know more now about getting the last play.

Bill Spight · Post by **Bill Spight** » Thu Sep 28, 2017 1:48 pm

Kano's beauty

Kano's final position for getting the last play is a thing of beauty.

Click Here To Show Diagram Code: [go]$$Wc Kano's beauty $$ ---------------------- $$ | . . . . . . . . . . . $$ | . . . . . . X X O . . $$ | . X . X . . X O . O . $$ | O X O X . X X O . , . $$ | X X X X . O X O . . . $$ | O X O . X O X O . . . $$ | O X . . X O X O . . . $$ | O O O O O . O . . . . $$ | . . . . . . . . . . . $$ | . . . , . . . . . , .[/go]

Kano's book may have been ghost written, but I believe that this position is Kano's invention. It combines a bread and butter hane-and-connect on the top side with a somewhat complicated position around E-15. As usual, we assume that the surrounding territory belongs to White. Kano has White to play.

Click Here To Show Diagram Code: [go]$$Wc Failure $$ ---------------------- $$ | . . . . . . . 6 4 5 . $$ | . . . . . . X X O . . $$ | . X . X . . X O . O . $$ | O X O X . X X O . , . $$ | X X X X 2 O X O . . . $$ | O X W . X O X O . . . $$ | O X 1 . X O X O . . . $$ | O O O O O 3 O . . . . $$ | . . . . . . . . . . . $$ | . . . , . . . . . , .[/go]

, saving the :wc:

stone, is a mistake. Black plays the sente, :b2:

, and then takes the hane-and-connect on the top side to get the last play.

Click Here To Show Diagram Code: [go]$$Wc White gets the last play $$ ---------------------- $$ | . . . . . . 8 7 9 . . $$ | . . . . . . X X O . . $$ | . X . X . . X O . O . $$ | O X O X 2 X X O . , . $$ | X X X X 1 O X O . . . $$ | O X W 6 B O X O . . . $$ | O X 4 5 B O X O . . . $$ | O O O O O 3 O . . . . $$ | . . . . . . . . . . . $$ | . . . , . . . . . , .[/go]

-

is correct, threatening the :bc:

stones, Black saves them and captures the :wc:

stone with reverse sente. Then White takes the hane-and-connect and gets the last play.

In this combination White can get the last play, regardless of who plays first.

Click Here To Show Diagram Code: [go]$$Bc Black sente $$ ---------------------- $$ | . . . . . . . . . . . $$ | . . . . . . X X O . . $$ | . X . X . . X O . O . $$ | O X O X . X X O . , . $$ | X X X X 1 O X O . . . $$ | O X W . X O X O . . . $$ | O X . . X O X O . . . $$ | O O O O O 2 O . . . . $$ | . . . . . . . . . . . $$ | . . . , . . . . . , .[/go]

Black has the obvious sente, leaving the hane-and-connect and the region around :wc:

miai. At first blush, then, this position is a Black sente. However, . . .

Click Here To Show Diagram Code: [go]$$Wc Ambiguous $$ ---------------------- $$ | . . . . . . . . . . . $$ | . . . . . . X X O . . $$ | . X . X . . X O . O . $$ | O X O X 2 X X O . , . $$ | X X X X 1 O X O . . . $$ | O X O 6 X O X O . . . $$ | O X 4 5 X O X O . . . $$ | O O O O O 3 O . . . . $$ | . . . . . . . . . . . $$ | . . . , . . . . . , .[/go]

After

-

White can simply leave the hane-and-connect unplayed. (Not when there is nothing else left on the board, OC.

) White's play is ambiguous between sente and reverse sente. This is a kind of ambiguity of which I was unaware.

moha · Post by **moha** » Fri Sep 29, 2017 8:26 am

Isn't the E15 area simply a double sente here? (with the complete sequences)

Bill Spight · Post by **Bill Spight** » Fri Sep 29, 2017 8:46 am

moha wrote:Isn't the E15 area simply a double sente here? (with the complete sequences)

It's ambiguously a double sente.

It is a sente for Black. White to play can choose whether to play it as a double sente or as a reverse sente.

moha · Post by **moha** » Fri Sep 29, 2017 11:09 am

Bill Spight wrote:
moha wrote:Isn't the E15 area simply a double sente here? (with the complete sequences)
It's ambiguously a double sente. It is a sente for Black. White to play can choose whether to play it as a double sente or as a reverse sente.

What is W's sequence when chose to play it as reverse sente?

Bill Spight · Post by **Bill Spight** » Fri Sep 29, 2017 12:41 pm

moha wrote:
Bill Spight wrote:
moha wrote:Isn't the E15 area simply a double sente here? (with the complete sequences)
It's ambiguously a double sente. It is a sente for Black. White to play can choose whether to play it as a double sente or as a reverse sente.
What is W's sequence when chose to play it as reverse sente?

Click Here To Show Diagram Code: [go]$$Wc White 1 pt. reverse sente $$ ---------------------- $$ | . . . . . . 8 7 9 . . $$ | . . . . . . X X O . . $$ | . X . X . . X O . O . $$ | O X O X 2 X X O . , . $$ | X X X X 1 O X O . . . $$ | O X O 6 X O X O . . . $$ | O X 4 5 X O X O . . . $$ | O O O O O 3 O . . . . $$ | . . . . . . . . . . . $$ | . . . , . . . . . , .[/go]

White keeps going after :b6:

to gain one point.

moha · Post by **moha** » Fri Sep 29, 2017 1:33 pm

Bill Spight wrote:
moha wrote:What is W's sequence when chose to play it as reverse sente?

$$Wc White 1 pt. reverse sente
$$ ----------------------
$$ | . . . . . . 8 7 9 . .
$$ | . . . . . . X X O . .
$$ | . X . X . . X O . O .
$$ | O X O X 2 X X O . , .
$$ | X X X X 1 O X O . . .
$$ | O X O 6 X O X O . . .
$$ | O X 4 5 X O X O . . .
$$ | O O O O O 3 O . . . .
$$ | . . . . . . . . . . .
$$ | . . . , . . . . . , .

Click Here To Show Diagram Code
[go]$$Wc White 1 pt. reverse sente $$ ---------------------- $$ | . . . . . . 8 7 9 . . $$ | . . . . . . X X O . . $$ | . X . X . . X O . O . $$ | O X O X 2 X X O . , . $$ | X X X X 1 O X O . . . $$ | O X O 6 X O X O . . . $$ | O X 4 5 X O X O . . . $$ | O O O O O 3 O . . . . $$ | . . . . . . . . . . . $$ | . . . , . . . . . , .[/go]

White keeps going after to gain one point.

Now I'm confused. This is the same sequence that is W's sente (for E15 area), isn't it? Or is there a different way for W if chose to play E15 area as double sente, as you mentioned?

And why is this reverse sente? B plays last there (E15 area), hence that part seemed simple double sente (with B's sente leaving a double gote there, W's sente nothing, and top being an independent double gote in any case)... :-?

Bill Spight · Post by **Bill Spight** » Fri Sep 29, 2017 1:50 pm

moha wrote:
Bill Spight wrote:
moha wrote:What is W's sequence when chose to play it as reverse sente?

$$Wc White 1 pt. reverse sente
$$ ----------------------
$$ | . . . . . . 8 7 9 . .
$$ | . . . . . . X X O . .
$$ | . X . X . . X O . O .
$$ | O X O X 2 X X O . , .
$$ | X X X X 1 O X O . . .
$$ | O X O 6 X O X O . . .
$$ | O X 4 5 X O X O . . .
$$ | O O O O O 3 O . . . .
$$ | . . . . . . . . . . .
$$ | . . . , . . . . . , .

Click Here To Show Diagram Code
[go]$$Wc White 1 pt. reverse sente $$ ---------------------- $$ | . . . . . . 8 7 9 . . $$ | . . . . . . X X O . . $$ | . X . X . . X O . O . $$ | O X O X 2 X X O . , . $$ | X X X X 1 O X O . . . $$ | O X O 6 X O X O . . . $$ | O X 4 5 X O X O . . . $$ | O O O O O 3 O . . . . $$ | . . . . . . . . . . . $$ | . . . , . . . . . , .[/go]

White keeps going after to gain one point.
Now I'm confused. This is the same sequence that is W's sente (for E15 area), isn't it? Or is there a different way for W if chose to play E15 area as double sente, as you mentioned?

The E-15 area by itself is more complicated. Adding the hane-and-connect actually simplified matters. The combination is a Black sente.

Click Here To Show Diagram Code: [go]$$Bc Black 1 pt. sente $$ ---------------------- $$ | . . . . . . . . . . . $$ | . . . . . . X X O . . $$ | . X . X . . X O . O . $$ | O X O X . X X O . , . $$ | X X X X 1 O X O . . . $$ | O X W . X O X O . . . $$ | O X . . X O X O . . . $$ | O O O O O 2 O . . . . $$ | . . . . . . . . . . . $$ | . . . , . . . . . , .[/go]

After

the hane-and-connect and the area around :wc:

are miai. End of story, locally.

For this to be a 1 pt. sente, White has to gain 1 pt. with a reverse sente. White does that with the above sequence.

White also has the option of stopping locally after :b6:

, for a double sente that gains no points.

And why is this reverse sente? B plays last there (E15 area), hence that part seemed simple double sente (with B's sente leaving a double gote there, W's sente nothing, and top being an independent double gote in any case)...

Yes, each of these two regions is independent. But their combination alters correct play. For instance, in combination with the hane-and-connect, :w1:

saving the :wc:

stone is incorrect, as Kano points out. White's only correct play is the one given.

All of the above assumes no ko fight, OC.

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