Good Empty Triangle

Joseki (a)  

is the vital point, even though it is an empty triangle.

Related joseki  

makes "good shape" but becomes overconcentrated.

unkx80: I don't think it's so much about overconcentration. I believe that it's got more to do with destroying White's eye shape.

Bill: Well, it is a question of emphasis, isn't it? Anyway, let's take away the stone.

brindis: Just a question, why not 2 at 'a'?

Serpent: Because doing so would open the black stone above 1 to atari.

(Sebastian:) I don't see that. That black stone has three liberties, reduces 's liberties to two, and it can easily be connected if need be.

Mutual good shape  

This is fine for both players, no? Black does not need an extra stone.

Eagle : Tewari analysis may show that the black shape is overconcentrated, but i think in practice the second diagram is nothing worse than the first one (i think it's better , may be just because i missed something ) .It's worse than the third diagram,not the first diagram . Am i wrong ?

corwin: To my eyes, the biggest difference in the two diagrams is that black ends in sente in the first, and gote in the second.

Joseki (b1)  

tderz: After the unreasonable cut , the continuation to gives Black the miai of either a or b,
hence is a 'good empty triangle'. (source: Ishida a.o.)

Joseki (b2)  

Similar is this 5-4 Joseki, where white's empty triangle would be a good tesuji to punish Black's overplay-cut: is an overplay, which empty triangle helps exploiting. After 4 moves, the cutting stones are capured. [source: D.Ormerot, http://gogameguru.com/5-4-openings]

Example - Joseki (c)

Joseki (c)  

(empty triangle) is often a good way to respond to White's 3-3 invasion in this shape.

(Sebastian:) Indeed, this is not uncommon, with 26 pro games played this way (according to SmartGo's library) only second to 'a', which occurs 49 times. And it occurs more frequently in games that led to a win. But why? What are its advantages over 'a'? (Later:) I found this discussed here, so I see some difference to 'a' now, but I'm still not convinced that it's superior.

Black to play  

This problem comes from the Tesuji Dictionary, by Segoe Kensaku and Go Seigen. They say that if you get this one right, you are 5 dan. (Of course, you have a big hint. ;-))

Solution

Good empty triangle  

The sequence of to is one of the best ways of escaping with the lone white stone at the top. makes the empty triangle and then White has a rather clear exit, while aiming for the cutting point at a (at the correct time).

Bad empty triangle  

here would be a mistake. plays at the vital point, destroying White's eye shape, and forcing to connect with a bad empty triangle.

Bob McGuigan: Here's an example from one of my own games (I was Black) where Black responds to a White empty triangle move by making one too. White's empty triangle looks good but after Black's response ...

2 empty triangles - is the 2nd one unnecessary?  

in response to is good defense. creates a cutting point in Black's shape. takes a liberty from White and leaves a lot of aji against White's group.

better a forcing move instead of an own empty triangle?  

tderz: Interesting position. (yet I think black's empty triangle is not necessary)
is tempting too - a & b seem miai now.
It is the same technique as in above joseki.

The white cut c seems far fetched with the created white weakness e.
If White wants to solidate first at at f, cutting through with black d would be possible
(resp. Bg, after white q, she cannot cut at r),
however, if replying with white d one has forced white to be very submissive (which is the intention of ) and could hane oneself with f.
Can White survive?

Yes, Wd - Be - Wg - Bf - then k (or l, smaller).

if Black tries too hard  

tderz: other ways for White to avoid an empty triangöle?
Perhaps not, after (protecting against the cut y) to , there is still no connection to the left , due to Black x (if Black a to white j have been exchanged),
but white cut capture at k and had no problems.

Theoretically, the black could become a target after ot , if Black tries too hard with black a to i?

 

tderz: is a good empty triangle.
This a game with many local "tenukis" - , , , even in succession ! -
for keeping the initiative.

fighting emty triangle - white's next move?  

tderz: from a Korean book, p.229 (ISBN 89-333-0346-4)
All black moves look completely natural, don't they? (except of course!)
Still he voluntarily created an empty triangle.
Should he have exchanged a for b first?

It's not so easy to decide on white's next move, hence the empty triangle can't be that bad and rather renamed fighting empty triangle.

The third "Ghost" of the "Blood Vomiting Game"  

is the third ghost move. It is an example of a "bad shape/good move", and eventually allows Jowa to launch a difficult splitting attack that results in Black's resignation.

Normal Life & Death

Numerous problems are based on the empty triangle move which kills with a nakade shape. Generally, bad shapes can turn good when captured, becoming inefficient eyespace for the opponent.

(Therefore it is dangerous to tell beginners that an 'empty triangle is bad'.
One can tell them, that an empty triangle is 'usually inefficient' - but only in the open field.

• surprisingly good empty triangle in Life & Death
• making an eye
• killing shape - san-moku-nakade?
• [ | ]

below from Killable Eye Shapes:

Shape #7.2: Three possible patterns for White.  

Number of internal points: 7
Required number of internal White stones to kill: 3
Remaining internal moves to capture: 14
Total internal liberties: 17
Other names: Butterfly Seven

Shape #7.3  

Number of internal points: 7
Required number of internal White stones to kill: 3
Remaining internal moves to capture: 14
Total internal liberties: 17

Shape #7.4  

Number of internal points: 7
Required number of internal White stones to kill: 4
Remaining internal moves to capture: 13
Total internal liberties: 17

From a classic collection

For examples of tactically brilliant empty triangles, see Xuanxuan Qijing Problem 297 and 302.

Endgame empty triangle

Ushinohama(W) vs Takemiya(B)  

Ushinohama responded with and Takemiya played , a sort of standard good shape move, but in a commentary he criticized as being really bad technique. Ushinohama played and Takemiya played tenuki with a large territorial move in the upper right corner(not shown in this diagram). This allowed Ushinohama to initiate the sequence White b, Black c, White d, which cost Black a lot on the lower side. Takemiya commented that should have been the empty triangle play at a, which would have been good shape in this situation and would not have allowed White to cross under with d.