Hane connect exercise 3 / Discussion

Normal Hane  

aLegendWai (9k? KGS): Correct me if wrong.

Nothing is wrong in this endgame play. Locally speaking (ie without considering the whole board), it is a typical and correct way to respond in the endgame.^[1001] Since white(W) is protected by the circled white stone. Nothing black(B) can do now.

(PS: In the question, it assumes that everything to the right is White's territory.)

Throw-in  

Bill: What if White plays a throw-in with ?

aLegendWai (9k? KGS): A very good question! It is another way to respond. Locally speaking, it gives the same result as the "normal hane" ^[1]. But it doesn't automatically mean they are equal. Reasons:

• although both the normal and trickier response give the same result
• the trickier one requires higher skills for B (and W as well) to play correctly
• if B responds wrongly, W will gain.
• throw-in may be used as a last-ditch way to play when W lags a bit behind B.

I will try to explain how B answers the throw-in.

Note:

• I illustrate in local sense only! So some global (whole-board) issues^[2] like tenuki (playing elsewhere) are ignored in the illustration.

B's response 1 - capture throw-in

Continued  

A ko fight over for one point. Locally speaking, B can only pass (there's no ko threat in the diagram!) and W wins the ko.

W keeps chasing it - wrong!  

B is happy to keep extending. When B extends by 1 stone, W keeps losing 2 points ().

Note: The loss of 1-point (at second line) occurs once B plays at . Afterward the 1-point loss keeps moving by 1 point to the right. So this loss is not counted to the loss of further B extension.

W's cut is impossible ( is captured)  

A cut of B by is of no use.

B's response 3a  

aLegendWai (9k? KGS): After extension, how W should respond then?

W has to grasp the only chance to play at the first line now. It is no longer possible if you miss that chance (due to the lack of the support of at the third line. This keeps B's invasion group 1 liberty).

B's response 3b  

B cannot connect at . W will cut and capture B's big group.

B's response 3d  

at .

Note:

• is not forbidden since it is not really a repetitive situation. It is somewhat a snapback.
• This website seems not to support double-digit number label (except 10). It would be much grateful if upload of SGF file is available to that website directly. I can thus explain and illustrate better.

Normal Hane  

HolIgor: Black has 4 points while white has 3 points. The score is -1. Black ended in gote.
aLegendWai (9k? KGS) Note: -1 is caluclated by the formula (W-B = 3-4). The reverse is possible, ie B-W = 4-3 = +1. It makes no difference to the result. The +/- simply denotes:

• -1 denotes W loses by 1 point(W-1)
• +1 denotes B wins by 1 point(B+1)
• In short, W-1 = B+1

Throw-in, capture  

HolIgor: Black will have to defend before connecting the ko. The score is 0. Black has 2 points plus 1 captured; white has 3 points. There is yet another possible point for white in the ko. So, white has already won a point and can add another.

Yet, this is gote for white.

ChrisSchack: Would it be a good idea for W to play a here immediately following?

Throw-in, nobi 3( captured by )  

aLegendWai (9k? KGS): Note:

• Read as .
  

HolIgor: Black has 2 points + 2 captured. White has 1 point + 2 captured. The score is -1. Black ended in gote. This is the same as the normal hane.

Sagari  

Let's look at the sagari first. After , - is sente. Whether this is better than - , depends upon the value of that sente as a ko threat versus the chance that White will get the reverse sente. With no ko, dominates.

White takes gote  

Now let's look at the throw-in. forces Black to fill eventually at a, but at what cost?

The cost is 1 2/3 points. That's how much worse this position is for White than the original position.

Miai (ii)  

The play could also go - , - . The value of the position remains the same.

At this point Black can fill the ko at to reach a position worth the same as after the sagari or the hane-tsugi (minus the ko threats on both sides). Filling is worth only 1/3 point, while the other plays are worth 2 points. So White's throw-in has allowed Black to gain 1 2/3 points for free.

Since the throw-in is bad, the hanetsugi is correct, subject to the qualifications concerning ko threats.

If B plays first - Normal Hane  

Black has 4 points while white has 3 points. The score is -1 (=W-B). Black ended in gote.
Note: -1 is caluclated by the formula (W-B = 3-4). The reverse is possible, ie B-W = 4-3 = +1. It makes no difference to the result. The +/- simply denotes:

• -1 denotes W loses by 1 point(W-1)
• +1 denotes B wins by 1 point(B+1)
• In short, W-1 = B+1

If W plays first - Normal Hane  

is used to protect the cut. Black has 1 point while white has 4 points. The score is +3 (=W-B). White ended in gote (in case if the sequence completes).

To find the value of this endgame, we have to compare the difference between B playing first and W playing first.

• If B first, socre = -1
• If W first, score = +3
• The difference = |(-1) - (+3)| = |-1-3| = |-4| = 4

Simple way  

I would say is the normal play here. There is still some aji at a, and usually it helps not to play out extra moves, if you are trying to leave the maximum aji.

One very theoretical example (Part 1)  

aLegendWai (9k? KGS): If 2 dead B stones () are in the W's territory...

One very theoretical example (Part 2)  

aLegendWai (9k? KGS): It is a theoretical example showing how dead stones can be alive (supposing W wrongly plays at ). After the sequence up to , it is likely for B to make a separate living group.
Note:
- Even if W doesn't play at , W cannot make any good ko fight (B can avoid any disadvantageous ko fight!).
- the cutting point is not a problem at all due to sufficient B liberties.

You may see a player forms a separate group (by similar skills in the endgame) from real games on the Internet although this kind of situations usually appears towards the end of another corner.