1. 3-3 invasion under a star point
Black’s descend at G19 is sente.
Black can kill the corner if white tenuki.
2. 3-3 invasion under a 4-4 large knight enclosure
This descend is sente.
3. 3-3 invasion under a 4-4 large knight enclosure
This descend is sente.
This is a multi-step ko for black.
4.
The order of white 1 and 3 can be reversed. With D19, black can kill white.
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