4-4 point 3-3 invasion joseki
For a first view of this joseki, see 3-3 Point Invasion. Players for whom this discussion goes too deep are advised to read that discussion instead. An overview of SL pages about the 3-3 point invasion is given on All About 33 Point Invasion.
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A 3-3 invasion of a 4-4 stone is one of the fundamental actions in go. It can take place at any time during the early opening to the late endgame. As with any joseki, the correct continuation and most successful outcome depends on nearby stones; and in the case of the 3-3 invasion, extensions away from the 4-4 stone and approaches toward the 4-4 stone play the most significant roles.
After , Black will block at either or . The general rule is to block on the wider side (i.e. the side with the most potential).
Following this, Black a hane leads to the hane-stretch and double hane variations, Black b jump leads to the jumping away variation, and Black c extend leads to the extend variation (see sections below). Tenuki is not recommended.
Black a is the traditional way of play, Black b is a modern innovation aimed at gaining sente, and Black c is an increasingly common move played when either Black b is unappealing or Black desires a more solid shape.
August 2018: It should be noted that the arrival of AI bots like AlphaGo, LeelaZero and ELF, which have achieved or surpassed professional strength, have made major shifts in the evaluation of positions and joseki. In particular, the 3-3 invasion is extremely popular with these bots and taking sente is very important. Hence, Black b has become almost the standard move and new variations have arisen from it, most of them trying to keep sente.
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.
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.
through form the basic continuation of this joseki in contemporary play (post-2016). Following this, Black a, Black b or tenuki are the most popular continuations. See 4-4 point 3-3 invasion, jumping away.
An increasingly common way to play when the jumping away variation is unappealing (post-2016). Black seeks a solid shape from these continuations. Following AlphaGo, White a has become fairly common, followed by White b and White c.
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.
The armpit hit of is a special continuation for when Black has superior outward influence and intends to either kill or severely attack White. , then begin the typical continuation, followed by a running battle for White's life. White cannot live by playing at a due to a tesuji.
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.
White cannot live by playing due to Black's tesuji at . The diagram shows one possible continuation after Black's tesuji. White may attempt to cut at a or b, or clamp at c, however in order to initially play , it was assumed that Black's outside influence was already sufficient enough to handle any running fight. If these continuations are viewed as too dangerous for Black, then he could even pull back at d, instead of playing . Therefore, these resistances by White are likely to fail.