There is an eye at a. If Black can connect the stone back, then White will be dead.
The blind spot is . Now White cannot capture the stone.
If blocks, then captures the White group including .
When clamps at the stone, connects the stone to the outside stones. Due to shortage of liberties, White cannot play at a.
The diagonal move at is an interesting one. But makes a and b miai.
The crawling in at is too simple, since can atari.
The cut at is too early. is the only correct reply (see Beginner Exercise 205). After , the three Black stones including is caught in a connect-and-die.
is a failure.
After , Black is caught in a double shortage of liberties.
here is also wrong.
After , Black cannot set up a snapback since playing at a places Black in self-atari.
here allows to block.
This cut at Black 3 does not work.