4-4 point one-space low pincer invasion, interception

Invasion, interception  

White's 3-3 invasion in response to Black's pincer is usually intercepted at . Up to this pattern has been standard ^[1] but Black's next move has changed from the solid connection a into the crawling move of . After avoids being locked into the corner, Black usually plays elsewhere although local moves are available too, such as b or c.

at d is an attractive looking hane at the head but is a mistake. ^[2]

Reasons for connecting underneath

The modern connection  

After AlphaGo, the choice of over a became the standard. The advantage is that White now cannot play at , either to connect her stone or cut off Black's wall from the rest of his position on the top, and the hane-connect of White b is not sente in the yose. The disadvantage is the possibility of the white cut at a.

Keima - honte answer  

With , Black extends his influence. Before the AI revolution was considered honte. Nowadays, it is considered slow and White would rather play elsewhere.

If White plays elsewhere  

If White does not answer , Black can exchange for . Before it was considered painful for White to allow Black this exchange in sente, but still it was seen e.g. Cho Chikun (Black) against Kobayashi Koichi in the 1999 Kisei title match.

Nowadays, the exchange doesn't seem to outweigh White's extra move elsewhere.

Pincer  

The tsume of is rarely played immediately. Nevertheless, it is a common manoeuvre for Black, as a follow-up.

After and , White has sente, but Black has confined her to the corner, and now has strength on both sides and towards the center.

Running into the center  

The alternative for White is to run into the center with and .

After ...

Continuation  

Black patches up his shape with . The continuation to is one possibility.

White has set her sights on the stones, but makes black thick in the center.

Overconcentrated  

is not a good move with the one-space low pincer. The stone is now too close to Black's wall.

Hane at the head  

The hane at the head feels natural but it is generally a mistake when is in place. White's best next move is the hane at 'a'.

There is an article about this shape that analyses it in some depth.

Countermeasure

Hane underneath  

aims to link up with . If connects solidly at , then at is probably even a better result for White.

White gets territory and sente. Black gets influence and cutting aji.

Clamp tesuji  

If and insist on cutting off then White has the clamp tesuji of . If Black draws back at , White connects at . Compared to the normal joseki, Black has made the extra exchange of for - which is aji keshi.

Black resists  

If Black tries to resist with , White cuts at . One possible follow-up is shown. If Black does not play at (but for example at ), White wins the semeai after White at -Black a - White b.

Continuation  

Black has been forced into a clumsy shape, while has been cut off and blighted. The four white stones are far from captured yet.

Wrong countermeasure

Wrong  

Many amateurs have learnt to answer with because if Black descends to , White fearlessly cuts at , either capturing three stones as in this diagram or capturing and making territory at the 4th line.

Countering the counter  

However Black can counter at and gets superior shape up to , trumping White's corner territory. Compared to the proper countermeasure Black is much better off here.