4-4 Point 3-3 Invasion, Hane
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The 4-4 Point 3-3 invasion, hane is a common move that is a feature of the traditional 3-3 invasion joseki? as well as double-hane joseki.
Playing hane at and stretch at is a classic and easy continuation. Black accepts gote in exchange for sufficient influence. Nowadays, the result is considered locally even; however, because White ends in sente it has led to Black more frequently adopting the jumping away variation to maintain sente (see Basic Continuation 3: Jumping Away).
Historically, invading the 3–3 point early in the game was considered bad because it was believed that this variation gave the non-invading player superior outward influence. However, AlphaGo showed that this assessment was incorrect and the outward influence was being overvalued by human players (i.e. the outward influence and inside territory are more balanced than previously thought). Several, new standard joseki were innovated by AlphaGo (and by subsequent professional play) and have since become extremely popular in both professional and amateur games. Responding to a 4-4 opening with a 3–3 invasion early in the game is now considered acceptable.
should be played before .
The crux of the redemption of the 3-3 invasion, is that after White omits a but instead crawls on the second line.
This gives White life in the corner and sente to play elsewhere. Black's wall is influential but not yet thick: it is lacking eyeshape. Therefore AI bots evaluate this exchange as favorable for White, despite "playing on the line of defeat (2nd line)".
This sequence marks the major deviation from traditional go theory by the AI bots. It has been adapted by human players, and now has mostly overtaken the traditional joseki above.
It is even possible for White to forsake and play tenuki immediately. Black has Black a as a continuation, to which White answers at b or c (exchanging for first if she hasn't done so already).
The double hane approach has more strict conditional requirements than the other continuations, usually played when the outside is no longer as profitable. The presence of nearby stones on the sides usually play a significant role in choosing this joseki and its subsequent continuations. See 4-4 point 3-3 invasion double hane.
A novel technique in pro games, beginning in the 2000s, is to play in preparation for the double hane. The intention of this move is to get extra thickness by shutting white off from both sides. It is mainly applied in cases where Black has a stone at a, b or c; that is, exactly when the crawling fight mentioned at the 4-4 point 3-3 invasion double hane would go poorly for Black. See 4-4 point 3-3 invasion joseki, hane and inside hane.
If White tries to reverse the order in the hane-stretch variation by playing before , then Black may punish with . This lets Black shut White into the corner (particularly as a is Black's sente). White ends up with a smaller corner (than in the joseki) and Black may be in a position to make territory on the left. The only positional disadvantage for Black is the aji of the cut at b. However, it general pales in comparison to White's initial loss and Black's overall gain. See 4-4 point 3-3 invasion, W reverse playing order.