3-4 point high approach low extension, trick play

Trick play setup.  

Table of contents White descends, black descends White descends, black hane up White atari

Table of diagrams Trick play setup. White descends, black descends. White cuts and is tricked Tricked, simple continuation Tricked and a further trick Further trick, cont'd Tricked, gote honte ending Black hane up at 8. White atari at 7. White atari, continuation The extension The extension

White descends, black descends

After white extends with , black normally plays . Alternatively, black can try to brew up trouble by playing c (See variations under 'White descends, black hane up')

White descends, black descends.  

The correct way to play for white is to give atari at a (see 3-4 point high approach low extension), but many players will be tempted to cut at b. This is a mistake.

Dieter: I have reviewed this "trick play" with Lizzie (Leela Zero and Katago). Both engines prefer this variation over the "correct" variation.

White cuts and is tricked  

After this sequence, may players will feel satisfied that they have captured the marked stone . In reality, they have been tricked.

Tricked, simple continuation  

One way for black to continue is to play like this. White gets only 4 or 5 points in the corner, while her marked stones () are cut off. Black is strong on both sides, so this result is terrible for white.

Dieter: AI prefer this variation, getting the corner in sente and the aji of the marked stones.

Tricked and a further trick  

Black can also continue with . This sets up another trick because the corner is not 100% alive yet. If, for example, white considers the corner alive and plays through . Black can kill the corner.

Herman: @Dieter, how does AI feel about this? Extending is, IMO, the main line for black. The atari in the previous diagram feels like a thank you move.

Further trick, cont'd  

After , white cannot play at a due to shortage of liberties

Tricked, gote honte ending  

Considering the above, white should play 1 to defend the corner. Now the p-q-r threat is gone, because the white capture at s then creates 2 liberties (r, t) instead of damezumari.

Herman: @Dieter: Specifically, this is considered the "correct" continuation after extending and now black gets sente (or he can use it to spend a move to encircle white's central stones)
The classification of above as "trick" or "obvious threat" is in the eye of the beholder.

White descends, black hane up

Black hane up at 8.  

After , the players are in for a complicated fight. White can avoid that fight by playing a, but playing a comprises a small loss for white.

Herman Hiddema: I will expand on this at a later time. For now, see the discussion at BQM186

White atari

White atari at 7.  

The white atari at 7 is a mistake. Black captures with .

White atari, continuation  

After black captures the stone at 3-3, white can only give atari with . After black defends, white has two cutting points. White will defend the upper cutting point at , after which black cuts with . With and , white sacrifices another stone and sets up a ladder. If the ladder is bad for white, this is a disaster, but even if it is good, black is very happy. Black gets a big corner in sente and can look forward to play a ladder breaker later on.

See also 3-4 point high approach low extension, whole board

The extension  

When White extends with , Katago postpones life in the corner, stressing central influence.

When connects at the circled point, Katago sees possible continuations at a, b or c, still not thinking about living in the corner.

Herman: Interesting. Killing the corner is a 20 point swing, but apparently the outside is bigger than that. Thanks for the insight!

The extension  

The countermeasure of is estimated as ~22% inferior by Katago.