Life In 19x19

Gotraskhalana wrote: In my previous post, I switched North and East and I also found a mistake. And this is exactly the reason why I am not sure of my results ...

Well, you found the mistake yourself.

BTW, these are the sequences I thought that you had in mind.

Sequences for Black's response:

$$Northern_connection
$$XOO.X..X.XXXX.-
$$..OX.....XO.O.-
$$XOOX....XOOO..-
$$OOOOX...7XO.O.-
$$XXOXX..6X1XOO.-
$$..X...954O2XO.-
$$......B80.X3XO-
$$............X.-
$$---------------

Click Here To Show Diagram Code

[go]$$Northern_connection
$$XOO.X..X.XXXX.-
$$..OX.....XO.O.-
$$XOOX....XOOO..-
$$OOOOX...7XO.O.-
$$XXOXX..6X1XOO.-
$$..X...954O2XO.-
$$......B80.X3XO-
$$............X.-
$$---------------[/go]

In the game, I had overlooked while reading ahead that White would need to come back to fix at the triangle. After this, I don't think that White has another forcing move, at least, I didn't find a way to get out / kill / seki with two moves although there are several possibilites to try. So, White gets five ko threats for the Northern connection.

$$Eastern_connection
$$XOO.X..X.XXXX.-
$$..OX.....XO.O.-
$$XOOX....XOOO..-
$$OOOOX...3XO.O.-
$$XXOXX...X2XOO.-
$$..X.....5W1XO0-
$$.......984X7XO-
$$........T.6.X.-
$$---------------

Click Here To Show Diagram Code

[go]$$Eastern_connection
$$XOO.X..X.XXXX.-
$$..OX.....XO.O.-
$$XOOX....XOOO..-
$$OOOOX...3XO.O.-
$$XXOXX...X2XOO.-
$$..X.....5W1XO0-
$$.......984X7XO-
$$........T.6.X.-
$$---------------[/go]

I thought that Black didn't need to respond to this because White cannot approach in the next move, but Black cannot approach, either. This gives a total of six ko threats, so Black should go for the Northern connection.

For reference:

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[go]$$Eastern_connection
$$XOO.X..X.XXXX.-
$$..OX.....XO.O.-
$$XOOX....XOOO..-
$$OOOOX...3XO.O.-
$$XXOXX...X2XOO.-
$$..X.....9W1XO8-
$$........54X7XO-
$$..........6.X.-
$$---------------[/go]

is an improvement for Black, in terms of the number of threats.

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[go]$$Eastern_connection
$$XOO.X..X.XXXX.-
$$..OX.....XO.O.-
$$XOOX....XOOO..-
$$OOOOX...3XO.O.-
$$XXOXX...X2XOO.-
$$..X......W1XO.-
$$........4.X.XO-
$$............X.-
$$---------------[/go]

Which means that is an improvement for White.

Question: Is there a difference in score between the two connections?

Your Eastern connection sequence *was* the sequence I had originally in mind. However, now I thought that it didn't work, so I will check it again.

Gotraskhalana wrote:Your Eastern connection sequence *was* the sequence I had originally in mind. However, now I thought that it didn't work, so I will check it again.

Ah, you're right.

Click Here To Show Diagram Code

[go]$$Eastern_connection
$$XOO.X..X.XXXX.-
$$..OX.....XO.O.-
$$XOOX....XOOO..-
$$OOOOX...3XO.O.-
$$XXOXX...X2XOO.-
$$..X...076W1XO.-
$$......9845X.XO-
$$........B...X.-
$$---------------[/go]

=

Congratulations!

Gotraskhalana wrote:... I messed up a corner because I tried to remember a joseki...

There is a proverb among go players that says "Learning joseki loses two stones strength". My personal phrasing of this is "Blindly memorizing joseki loses two stones strength".
The second - and less widely known - part of the proverb is "Understanding joseki gains four stones strength".

Sensei's library has more on this idea: http://senseis.xmp.net/?LearningJosekiL ... esStrength


With this concept in mind, let's look at the joseki that you played.

With your first move, you are saying "I want the corner, with maybe a little possibility of outside influence."

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[go]$$B
$$------------
$$-.........
$$-.........
$$-..a......
$$-..B,.....
$$-.........
$$-.........
$$-.........[/go]

( If you wanted an ironclad grip on the corner, you would have played the 3-3 point at 'a'. )


With his reply, white says "OK, you can have the corner, I'll settle for outside influence".

Click Here To Show Diagram Code

[go]$$W
$$------------
$$-.........
$$-.........
$$-.........
$$-..X,W....
$$-.........
$$-.........
$$-.........[/go]

With your next move, you are telling white "No! You can't have easy outside influence. I'm going to go outside of you, and I'm also going to deprive you of eye space." This is a confrontational move.

Click Here To Show Diagram Code

[go]$$W
$$------------
$$-.........
$$-.........
$$-....a.B..
$$-..X,O....
$$-.........
$$-...b.....
$$-.........[/go]

( You could have repeated your claim to corner territory with 'a', or you could have played a peaceful move like 'b', going for some territory in the corner and the possibilities of both influence and territory on the left side. Both are solid, time-tested joseki. )


White now gets into the spirit of the moment, being just as confrontational. "You wanna play tough guy? OK, if I can't have easy influence, you can't have easy territory".

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[go]$$W
$$------------
$$-.........
$$-.........
$$-..W...X..
$$-..X,O....
$$-.....a...
$$-.........
$$-.........[/go]

( White could have played more peacefully at 'a', which is another joseki )


Your next move is again very confrontational. "No, you can't have influence, and you can't have my corner either. I'll cut you apart! You are going to die!!"

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[go]$$W
$$------------
$$-.........
$$-.........
$$-.aOB..X..
$$-..X,O....
$$-.........
$$-.........
$$-.........[/go]

( A safe play at 'a' is also joseki )


White has no choice. He must cut. You both are now caught in the current of your own making.

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[go]$$W
$$------------
$$-.........
$$-.........
$$-..OX.X..
$$-..XWO....
$$-.........
$$-.........
$$-.........[/go]

You have no choice but to extend. All of this macho posturing has resulted in a situation in which nobody can back down.

Click Here To Show Diagram Code

[go]$$W
$$------------
$$-.........
$$-.........
$$-..OXB.X..
$$-..XOO....
$$-.........
$$-.........
$$-.........[/go]

White says "You like cuts? Here, suck on this!" White needs to play this so that C18 is sente. White can't do anything less aggressive, or black gets ahead.

Click Here To Show Diagram Code

[go]$$W
$$------------
$$-.........
$$-.........
$$-..OXXWX..
$$-..XOO....
$$-..a......
$$-.........
$$-.........[/go]

( White can also play 'a'. FWIW, I followed Bill's advice and played around with this joseki. It turns out that he must eventually do both. Which comes first hardly matters, I think )


Again, you chose the most aggressive move. "I'm gonna kill something!"

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[go]$$W
$$------------
$$-.........
$$-.....a...
$$-..OXXOX..
$$-..XOOB...
$$-.........
$$-.........
$$-.........[/go]

( You could have chosen the more stable play at 'a'. )


White (to himself): "Maybe I can distract this homicidal maniac by giving him another stone to chase."

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[go]$$W
$$------------
$$-.........
$$-.....W...
$$-..OXXOX..
$$-..XOOX...
$$-.........
$$-.........
$$-.........[/go]

Black(to himself): "This is getting crowded. First I must get some more room for me. Then I can resume attacking white."

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[go]$$W
$$------------
$$-.........
$$-..X..O...
$$-..OXXOX..
$$-..XOOX...
$$-.........
$$-.........
$$-.........[/go]

White: "I'm not going to let you have an easy kill here either."

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[go]$$W
$$------------
$$-.........
$$-..X..O...
$$-.WOXXOX..
$$-..XOOX...
$$-.........
$$-.........
$$-.........[/go]

Black: "Die, you scum, DIE!!!"

Click Here To Show Diagram Code

[go]$$W
$$------------
$$-.........
$$-..X..O...
$$-.OOXXOX..
$$-.BXOOX...
$$-.........
$$-.........
$$-.........[/go]

White: "You must have overdosed on your anti-psychotic meds. I'll put you out of your misery."

Click Here To Show Diagram Code

[go]$$W
$$------------
$$-.........
$$-..XW.O...
$$-.OOXXOX..
$$-.XXOOX...
$$-.........
$$-.........
$$-.........[/go]

That is what pros are thinking when they play that joseki. It is a very aggressive sequence by both sides. ( Are you aware that you were playing one of the most aggressive versions? Or do you simply play it because everyone else is playing it? )

If you take the time to understand the meaning of each move that you play, you would see that you must play D18 or E18. Black's previous move was an attempt to get more space. One of those two moves would have been the natural follow up.

Joaz Banbeck wrote: That is what pros are thinking when they play that joseki. It is a very aggressive sequence by both sides. ( Are you aware that you were playing one of the most aggressive versions? Or do you simply play it because everyone else is playing it? )

If you take the time to understand the meaning of each move that you play, you would see that you must play D18 or E18. Black's previous move was an attempt to get more space. One of the suggested moves would have been the natural follow up move.

Thanks a lot for this instructive and delightful explanation.

For further context: I played this version on purpose because I did some exercices on it on Guo Juan's website and I wanted to try it out and see what to do with it afterwards. I switched to the "kill" idea in the end because I did do actual reading in between and this is the kind of reading error I do.

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[go]$$B
$$-------------------
$$| . . . . . . . . .
$$| . . X . . O . . .
$$| . W O X X O X . .
$$| . . X O O X . . .
$$| . . . . . . . . .
$$| . . . . . . . . .[/go]

Click Here To Show Diagram Code

[go]$$B Joseki
$$-------------------
$$| . . . . . . . . .
$$| . . X . 1 O 3 . .
$$| . O O X X O X . .
$$| . . X O O X 5 . .
$$| . . 2 . . 4 . . .
$$| . . . . . . . . .[/go]

Resulting shape (joseki):

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[go]$$B
$$-------------------
$$| . . . . . . . . .
$$| . . X . X O X . .
$$| . O O X X O X . .
$$| . . X O O X X . .
$$| . . O . . O . . .
$$| . . . . . . . . .[/go]

Thanks for your replies.

I bought "Get Strong at the Endgame" and started to do the problems that one is supposed before and after reading the book. I am pretty sure that I get the best answers while playing around on the board, but I get them only because I *know* that the color I am playing is probably not supposed to lose by one point.

Also, I tried again to look at some pro games. They still don't make much sense, but I can tell that the first few moves might be helpful to try out some other fuseki. But in many games, they leave groups all over the place that look dead and dying which is obviously possible with good reading abilities, but not really something to emulate.

Gotraskhalana wrote:3. New situation. During the fuseki, I ignored the following second-line play by my opponent:

$$B
$$------------
$$|.........
$$|.....7...
$$|..35.1.2.
$$|.94O6....
$$|......8..
$$|.........
$$|.........
$$|.........
$$|.........
$$|..O......

Click Here To Show Diagram Code

[go]$$B
$$------------
$$|.........
$$|.....7...
$$|..35.1.2.
$$|.94O6....
$$|......8..
$$|.........
$$|.........
$$|.........
$$|.........
$$|..O......[/go]

So, later on, we had the follow-up move:

$$B
$$------------
$$-.........
$$-.....X...
$$-..XX.X.O.
$$-.XOOO....
$$-......O..
$$-.B.......
$$-.........
$$-.........
$$-.........
$$-..O......

Click Here To Show Diagram Code

[go]$$B
$$------------
$$-.........
$$-.....X...
$$-..XX.X.O.
$$-.XOOO....
$$-......O..
$$-.B.......
$$-.........
$$-.........
$$-.........
$$-..O......[/go]

In the game, bad things happened, ending up like this (stopped only by my next stones waiting near the far corner:

$$W
$$------------
$$-..O......
$$-.OXXXX...
$$-.OXXOX.O.
$$-XXOOO....
$$-435...O..
$$-.B1......
$$-XX2O.....
$$-.XOO.....
$$-.XXO.....
$$-.XO......
$$-.XO......
$$-.XXO.....
$$-.OO......
$$-...O.....

Click Here To Show Diagram Code

[go]$$W
$$------------
$$-..O......
$$-.OXXXX...
$$-.OXXOX.O.
$$-XXOOO....
$$-435...O..
$$-.B1......
$$-XX2O.....
$$-.XOO.....
$$-.XXO.....
$$-.XO......
$$-.XO......
$$-.XXO.....
$$-.OO......
$$-...O.....[/go]

After the game, I concluded that is my first response move that was the problem and I should stop black from further away. After the first move, it seems to me that I could not have done much better and maybe I should have tenuki'd.

I submit that the problem was the original tenuki.

Click Here To Show Diagram Code

[go]$$B
$$------------
$$|.........
$$|.....X...
$$|.3XX.X.O.
$$|.1OOO....
$$|.2....O..
$$|.a.......
$$|.........
$$|.........
$$|.........
$$|..O......[/go]

is not certain, but is very likely. Depending on the rest of the board, White might tenuki in this situation. The clamp at "a" is not nearly the threat that the jump to "a" was in the actual game.

Bill Spight wrote:Question: Is there a difference in score between the two connections?

Answer hidden for those who want to work it out for themselves.

I have not yet thought about the score question because initially it didn't make sense to me. I have realized now that the question is what Black needs to do/have done when the corner is played.

Will think about it later.

Thanks for your explanation.

Now, for something new from a current game.

I needed ko threats against this corner (two would have been enough, actually):

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

I played the following sequence of ko threats and answers (moves around the ko are omitted):

Click Here To Show Diagram Code

[go]$$B
$$ | . . . . . . . . .
$$ | . . . . . . . . .
$$ | . . . . . . . . .
$$ | . . X . . . . . .
$$ | . X . . . . . . .
$$ | . O X X . . . . .
$$ | . O O O X X X . .
$$ | 8 . 2 1 O O X . .
$$ | . . 6 3 7 5 . . .
$$ ------------------[/go]

So, I think that I could do better. It seems that this works, but after that I don't see a third ko threat:

Click Here To Show Diagram Code

[go]$$B
$$ | . . . . . . . . .
$$ | . . . . . . . . .
$$ | . . . . . . . . .
$$ | . . X . . . . . .
$$ | . X . . . . . . .
$$ | . O X X . . . . .
$$ | . O O O X X X . .
$$ | . 3 1 2 O O X . .
$$ | . . . . . 5 . . .
$$ ------------------[/go]

Maybe starting from the outside:

Click Here To Show Diagram Code

[go]$$B
$$ | . . . . . . . . .
$$ | . . . . . . . . .
$$ | . . . . . . . . .
$$ | . . X . . . . . .
$$ | . X . . . . . . .
$$ | . O X X . . . . .
$$ | . O O O X X X . .
$$ | . . . . O O X . .
$$ | . 3 . 2 . 1 . . .
$$ ------------------[/go]

3 looks pretty scary without a response, but I find it hard to be sure that I checked all responses properly, much less finding the response that generates the least subsequent ko threats.

Gotraskhalana wrote: I needed ko threats against this corner (two would have been enough, actually):

I have it on good authority now that the answer is 5 or 4, depending on whether the defender accepts seki. I will try to recover the sequences later.

I played low Chinese and got destroyed by the following move. In the meantime, I found responses without dying all over a quarter of the board by one liberty, but I have not found a response that I am really happy with.

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[go]$$W
$$...,...-
$$....X..-
$$.......-
$$.......-
$$.......-
$$...31..-
$$.4.,2..-
$$..5X...-
$$.......-
$$.......-
$$--------[/go]

I think that either 3 is already wrong or 7 should be above 5, but I can't say I like the result because I still need to fight for the life of the corner.

Click Here To Show Diagram Code

[go]$$B
$$....,...-
$$.....X..-
$$........-
$$........-
$$........-
$$....OO..-
$$..X12X..-
$$754OX3..-
$$86......-
$$........-
$$---------[/go]

Gotraskhalana wrote:I played low Chinese and got destroyed by the following move. In the meantime, I found responses without dying all over a quarter of the board by one liberty, but I have not found a response that I am really happy with.

$$W
$$...,...-
$$....X..-
$$.......-
$$.......-
$$.......-
$$...31..-
$$.4.,2..-
$$..5X...-
$$.......-
$$.......-
$$--------

Click Here To Show Diagram Code

[go]$$W
$$...,...-
$$....X..-
$$.......-
$$.......-
$$.......-
$$...31..-
$$.4.,2..-
$$..5X...-
$$.......-
$$.......-
$$--------[/go]

5 is almost certainly an overplay, particularly if he doesn't help his outside group first (this is of course assuming white does not have support on the lower side). That doesn't mean you can kill it, but as it squirms for life you should be able to get stronger and 1 and 3 wither and die. However, there is indeed some bad aji here that white might reasonably exploit later once the outside stones are safe. Something worth mentioning is black 4 can be played one point to the right as kosumi instead of knight's move if you need to be more solid.

Gotraskhalana wrote: I think that either 3 is already wrong or 7 should be above 5, but I can't say I like the result because I still need to fight for the life of the corner.

$$B
$$....,...-
$$.....X..-
$$........-
$$........-
$$........-
$$....OO..-
$$..X12X..-
$$754OX3..-
$$86......-
$$........-
$$---------

Click Here To Show Diagram Code

[go]$$B
$$....,...-
$$.....X..-
$$........-
$$........-
$$........-
$$....OO..-
$$..X12X..-
$$754OX3..-
$$86......-
$$........-
$$---------[/go]

3 is correct, the only move. If white captures the corner stone his 2 stones get a lot stronger and yours weaker. Ladder the outside stone and lose the corner is great for white, it's robbery not a trade! 7 is probably ok and the normal move, though it helps if you have the ladder if white cuts. You shouldn't collapse if you don't have the ladder, but if white can cut the fighting can get complex and not so miserable for white. If white didn't cut then the crawl of 8 above is possibly a mistake because black has a powerful descent of 3 below white threatens to take 2 stones and ruins white's shape*:

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[go]$$B
$$ , . . . . . , . . . |
$$ . . . . . . . X . . |
$$ . . . . . . . . . . |
$$ . . . . . . . . . . |
$$ . . . . . . . . . . |
$$ . . . . . . O O . . |
$$ , . . . X X O X . . |
$$ . . 1 X O O X X . . |
$$ . . 2 O . . 3 . . . |
$$ . . . . . . . . . . |
$$ --------------------+[/go]

If white connects then black can extend and white has to crawl on the 2nd line for a long time to make life or have any hope of winning a semeai on the corner starting with a. Black's corner isn't alive yet though so you can't extend on the 3rd line forever and let white live in sente or he can play a, so you might need to tenuki eventually and hane (hanging) connect at b. This not only lives but creates a cut and further weakens white's 3 stones there, so if white then follows up on the lower side you can kill them.

Click Here To Show Diagram Code

[go]$$B
$$ , . . . . . , . . . |
$$ . . . . . . . X . . |
$$ . . . . . . . . . . |
$$ . . . . . . . . . . |
$$ . . . . . . . . . . |
$$ . . . . . . O O b . |
$$ , . . . X X O X a . |
$$ 7 5 1 X O O X X . . |
$$ . 6 2 O 4 . 3 . . . |
$$ . . . . . . . . . . |
$$ --------------------+[/go]

White could sacrifice the cutting stones to get out, but black is probably happy to capture them and connect. White now has 2 weak groups. If black doesn't like this he shouldn't descend but extend again.

Click Here To Show Diagram Code

[go]$$B
$$ , . . . . . , . . . |
$$ . . . . . . . X . . |
$$ . . . . . . . . . . |
$$ . . . . . . . . . . |
$$ . . . . . . . . . . |
$$ . . . . . . O O . . |
$$ , . . . X X O X . . |
$$ . 4 1 X O O X X . . |
$$ . . 2 O 5 . 3 . . . |
$$ . . . . . . . . . . |
$$ --------------------+[/go]

So if the white crawl is probably a mistake then what is better? "My opponent's key point is my key point" applies: hane to the corner. Black should block or else his 2 stones suffer and then white can crawl; white having, in sente, stopped black destroying his eye shape in sente with the descent.

Click Here To Show Diagram Code

[go]$$B
$$ , . . . . . , . . . |
$$ . . . . . . . X . . |
$$ . . . . . . . . . . |
$$ . . . . . . . . . . |
$$ . . . . . . . . . . |
$$ . . . . . . O O . . |
$$ , . . . X X O X . . |
$$ . . 1 X O O X X . . |
$$ . . 4 O . . 2 3 . . |
$$ . . . . . . . . . . |
$$ --------------------+[/go]

Next black probably extends, and white can crawl again or save the stone, which makes/takes eyes for both. Black now needs to take care of his corner. Locally speaking the hanging connection of 9 is not alive yet whilst descent is ko, but white needs to fix the cut on the outside first before going to kill (it is quite annoying if white can fix in sente later). However the lower side white group isn't alive yet either and depending on the continuation black might get a or the hane in sente.

Click Here To Show Diagram Code

[go]$$B
$$ , . . . . . , . . . |
$$ . . . . . . . X . . |
$$ . . . . . . . . . . |
$$ . . . . . . . . . . |
$$ . . . . . . . . 8 . |
$$ . . . . . . O O 7 . |
$$ , . . . X X O X . 9 |
$$ . 5 1 X O O X X . . |
$$ . . 4 O . 6 2 3 . . |
$$ . . . . . . . a . . |
$$ --------------------+[/go]

Probably white would then crawl on the lower side and black might extend or do something on the right.

Click Here To Show Diagram Code

[go]$$W
$$ , . . . . . , . . . |
$$ . . . . . . . X . . |
$$ . . . . . . . . . . |
$$ . . . . . . . . . . |
$$ . . . . . . . . O . |
$$ . . . . . . O O X . |
$$ , . . . X X O X . X |
$$ . X X X O O X X . . |
$$ . 1 O O . O O X . . |
$$ . . . . . . . . . . |
$$ --------------------+[/go]

If white did defend the cut and try to harass the corner then black could peep or5 turn (note how the hane of 4 in sente makes the corner alive):

Click Here To Show Diagram Code

[go]$$W
$$ , . . . . . , . . . |
$$ . . . . . . . X . . |
$$ . . . . . . . . . . |
$$ . . . . . . . 1 . . |
$$ . . . . . . . . O . |
$$ . . . . . . O O X . |
$$ , . . . X X O X . X |
$$ 6 X X X O O X X . . |
$$ . 3 O O 5 O O X 8 . |
$$ . . . . 2 . 4 7 . . |
$$ --------------------+[/go]

Click Here To Show Diagram Code

[go]$$W
$$ , . . . . . , . . . |
$$ . . . . . . . X . . |
$$ . . . . . . . . . . |
$$ . . . . . . . 1 . . |
$$ . . . . . . . . O . |
$$ . . . . . . O O X . |
$$ , . . . X X O X . X |
$$ . X X X O O X X . . |
$$ . 2 O O . O O X . . |
$$ . . 5 . 3 . 4 . . . |
$$ --------------------+[/go]

* one key reason why white having the ladder helps is black's descent is no longer possible without extend one more time as white can get sente ataris before coming back to connect, or capture black in a ladder:

Click Here To Show Diagram Code

[go]$$B 7 is not fast enough now
$$ , . . . . . , . . . |
$$ . . . . . . . X . . |
$$ . . . . . . . . . . |
$$ . . . . . . . . . . |
$$ . . . . 5 . . . . . |
$$ . . . 4 3 . O O . . |
$$ , . 9 2 X X O X . . |
$$ . 8 1 X O O X X . . |
$$ . . 6 O . . 7 . . . |
$$ . . . . . . . . . . |
$$ --------------------+[/go]

Edit 2018: Michael Redmond 9p talked in detail about this shape in this AlphaGo game review: https://youtu.be/3d00lk-U-ss?t=19m52s

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[go]$$W Simple and strong
$$ . , . . . . . , . . . |
$$ . . . . . . . . X . . |
$$ . . . . . . . . . . . |
$$ . . . . . . . . . . . |
$$ . . . . . . . . . . . |
$$ . . . . . . . O O . . |
$$ . , . . 2 X X O X . . |
$$ . . . . . 1 O X X . . |
$$ . . . . . . . . . . . |
$$ . . . . . . . . . . . |
$$ ----------------------+[/go]

is simple and strong.

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[go]$$Wm3 Tesuji
$$ . , . . . . . , . . . |
$$ . . . . . . . . X . . |
$$ . . . . . . . . . . . |
$$ . . . . . . . . . . . |
$$ . . . . . . . . . . . |
$$ . . . . . . . O O . . |
$$ . , 4 8 X X X O X . . |
$$ . 5 3 2 7 O O X X . . |
$$ . . . 1 . 9 6 . . . . |
$$ . . . . . . 0 . . . . |
$$ ----------------------+[/go]

is tesuji.

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[go]$$B Threat
$$ . , . . . . . , . . . |
$$ . . . . . . . . X . . |
$$ . . . . . . . . . . . |
$$ . . . . . . . . . . . |
$$ . . . . . . . . . . . |
$$ . . . . . . . O O . . |
$$ . , X X X X X O X . . |
$$ . O O X O O O X X . . |
$$ . . 5 O 1 O X . . . . |
$$ . . . . 2 3 X . . . . |
$$ ----------------------+[/go]

connects

The first line descent carries a strong threat.

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[go]$$Wm13 White is heavy
$$ . , . . . . . , . . . |
$$ . . . . . . . . X . . |
$$ . . . . . . . . . . . |
$$ . . . . . . . . . . . |
$$ . . . . . . . . . . . |
$$ . . . . . . . W W . . |
$$ . , X X X X X W X . . |
$$ . O O X O O O X X . . |
$$ . . . O . O X 1 2 . . |
$$ . . . . . . X . . . . |
$$ ----------------------+[/go]

prevents Black's threat with sente, but at the cost of letting Black secure the corner. White has sente, but now the stones are heavy.

There are more complicated fights, OC, but this is an easy way for Black to gain an advantage.