4-4 point low approach, high extension, invasion  

White has three standard answers to deal with the invasion: contain immediately by attaching at a, or reinforce first by attaching at b or, as surfaced from the AI revolution by forcing at c.

Other options to investigate are d, attacking , e dodging the invastion and f jumping out.

Attach and contain

Wedge and settle  

The wedge variation usually results in White influence, while Black will settle at the , by continuing to push or jump at some point, depending on stones present to the right.

Wedge and ladder issue  

White can also atari from below, resulting in a variation which can result in ko at and ladder at a.

Attach and take corner

Corner  

This attachment turns into a variation of the 4-4 point, low approach. With the marked stones present, White may choose to take the corner at instead of connecting at .

Force

Force  

Forcing with is an AI novelty. We get a wedge variation next.

Invading

Invasion  

Aside from local responses, immediately seeking compensation in the corner is possible. However, Black may turn here and confine White into the corner, especially if Black has a stone at the circled spot. After , White's marked stone is oddly placed.

Stretch  

From Lee Sedol's Go invasion et reduction: White can live in Black's moyo.

AI move  

When analyzing this position, LZ prefers here, taking the corner and some centre influence in sente to then play .

Clamping and sacrifice tactics  

From Takagi Kato invasion clamp and sacrifice