4-4 Point Low Approach Low Extension, Contact, Atari Down

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The 4-4 point low approach low extension, contact, atari down is part of the most common sequence in the AI 4-4 small knight approach joseki.

It is usually played Black to emphasize influence towards the left side of the board. It is also possible for Black attempt switching the direction of play to the top side, although this will often result in a fight.

This position is urgent and Black cannot tenuki.

Table of contents Quick Navigation Overview Default Side Switch Sides Discussion When to switch sides? When not to switch sides? What's the difference between the tiger's mouth and the connect-push for influence? References

Quick Navigation

Moves are listed by frequency in professional games^[1], which is sensitive to whole-board position. Bolded moves are commonly considered joseki.

Atari Down Joseki  

• a, Connect (~63%) - (joseki) (common) (AI favorite)
• b, Descend (~19%) - (joseki) (situational)
• c, Tiger's Mouth (~18%) - (joseki) (common) (transposition)

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Overview

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Default Side

Default Side Variations
Influence Var. (~42%)[1]	Influence Var. (~42%)[1]	Territory Var. (~25%)[1]	White Resists (~1%)[1]

• Connecting with usually gives Black the option to prioritize influence (Dia 1) or territory (Dia 3).
• The Tiger's Mouth with transposes to the influence variation (Dia 2).
• It is possible for White to resist Black's plans by capturing the corner with (Dia 4). This is usually inferior for White on an empty board, as the final result makes Black too thick. However, it is a legitimate possibility if the top side of the board has poor potential. This variation is rarely seen in professional games, as Black should avoid the "atari down" joseki to begin with if the top side of the board has little value. Black can continue with at a for sente or b for better outside shape.

Switch Sides

Switch Side Variations
Universal Stem (~18%)[1]	Main Var. (~15%)[1]	Cut Var. (~1%)[1]

• Descending with cedes the corner to White and takes the outside influence. The most common sequence played in professional games is depicted in Dia 2. However, White has two cutting stones that retain significant aji. Historically, it was believed that White should not move those stones prematurely, but in the AI era, White is often advised to move out with those stones immediately. This provokes a fight whereby Black has two weak groups on the sides whereas White has one weak group in the center. In some variations, Black might opt to neglect one side in order to focus on the side with more potential. Obviously, this is very sensitive to the board context.
• The first branching point in this joseki is shown in Dia 1. Option a is most common. Option b typically transposes to the Main Variation, but it is played when White wants to avoid the Cut Variation (Dia 3). Option c is joseki when White has an additional stone at the marked square, in which case the descend is a mistake, as White can win the capturing race outright as explained below in the Discussion section.
• It is possible for White to tenuki after completing the Main Variation (Dia 2). It is White's privilege to re-activate the aji at a, although AI programs often take advantage of this opportunity early.
• The Cut Variation (Dia 3) is more frequently played when Black is confident about the resulting fight, particularly when Black has supporting stones on the sides.

Discussion

When to switch sides?

Gu Zihao (9p) (B) vs. Li Weiqing (9p) (W) (2023)
Turn 19	Turn 32

yuzukitea: The descend to switch sides is a move that professionals play in a variety of circumstances, including on an empty board for apparently no reason. It is usually not AI's top choice on an empty board, and it involves a local loss, but professionals seem to believe that it is playable in the early opening even with little surrounding context.

In the AI era, this move demonstrates fighting spirit. This joseki produces two cutting stones that were previously believed to have little vitality, but the AI revolution has changed popular perspectives among professionals. It is now common for the approaching player to run with the cutting stones immediately, which initiates a fight. This fight usually involves two weak groups along the sides for the defender and one weak group in the center for the approacher. It is difficult for the defender to manage both sides at the same time, and usually the approacher will gain something on one side or the other.

Three circumstances may make this joseki choice especially appealing for the defender:

    (1) The opposite (non-default) side of the board is interesting or hot.

    (2) The defender has one or more stones that can assist with a fight on either side.

    (3) The defender has potential on both sides of the board.

Gu Zihao vs. Li Weiqing (2023) illustrates a game where all of these criteria are fulfilled. In this board example, the left side of the board is very hot due to the fact that Black's stones are unsettled. Earlier, White had pincered earlier with . If White now descends with at a, the stone shines brightly because White's resulting group on the left side is no longer weak. At the end of the this sequence, White would only have one weak group to handle (the top side), whereas Black has two weak groups to handle (the center group and the stones), which is clearly favorable for White.

The descend joseki can be played even when the defender lacks supporting stones, but the result is much sweeter when the conditions are favorable.

However, be warned that there are some other circumstances when the descend joseki is a mistake.

When not to switch sides?

Excerpt from AI Weiqi Joseki Dictionary  

According to Jiang Weijie's AI Weiqi Joseki Dictionary, if White possesses an existing stone around the vicinity of the marked position , Black cannot descend with .

White can play the nonstandard move and Black loses the capturing race outright.

More generally speaking, it is probably unfavorable for Black to descend if the resulting fight seems unfavorable, such as when White has additional stones in the vicinity for support. Additionally, there is little reason to pursue the descend variation if Black lacks potential towards the sides of the board.

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What's the difference between the tiger's mouth and the connect-push for influence?

Excerpt from AI Weiqi Joseki Dictionary  

yuzukitea: If Black intends to go for influence, the tiger's mouth with typically transposes to the connect-push variation. The differences between the order of these two moves is so subtle that its hardly worth discussing except as trivia, but we'll break down the nuances regardless.

The tiger's mouth with discourages White from capturing the corner with . According to Jiang Weijie's AI Weiqi Joseki Dictionary, preserves Black's thickness. Later on, if White chooses to tenuki too many times, the atari at a could make White's corner uncomfortable. White has a slightly better outcome if White captures the corner after the connect at z.

All of this being said, in most circumstances, it is considered inferior for White to capture the corner anyways. Why would Black want to prevent White from making an inferior move? Strategically, it's irrelevant in most circumstances, which is why AI programs often evaluate the tiger's mouth and connect-push equivalently.

The only exception would be the rare circumstances when it is a good move for White to capture the corner (e.g. the bottom side has little value). If the bottom side has little value, the tiger's mouth is a method for Black to maximize influence towards the left side, even at the price of ceding the corner territory.

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References

[1] Frequency statistics were obtained from professional games downloaded from kifudepot? (Jan 2016 - Nov 2023) constrained to a local search.

[2] AI Weiqi Joseki Dictionary (2021) by Jiang Weijie