3-4 point high approach low extension, cross-cut
The sequence formerly known as trick play
After , is a normal response. is normally played at . When cuts here, the continuation to is almost forced.
Before AI it was believed in the previous diagram should be played as here. AI however thinks this thick terriroty in sente for Black is too good.
There are however many fighting variations
White gets territory, albeit small, in sente. The confined position was long believed to be inferior but AI has evaluated this more positively for White.
Black can extend at . For a long time this was thought to set up a trap by extending later at a, catching White in a shortage of liberties after b and c. However, AI seems to have found a countermeasure. Up to White plays with the idea to sacrifice the corner and get a favorable position in the center, should Black activate the aji at a.
After it's Black who suffers from shortage of liberties
On a whole board like this, AI 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.
Killing the corner is a 20 point swing, but apparently the outside is bigger than that.
The countermeasure of is estimated as ~22% inferior by Katago.
White descends, black hane up
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.
See the discussion at BQM186
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.