Black can choose the next move between A and B.
Later, there are the right of black, A or B.
And later, there is a gote end game zone.
White 2 is very important.
The sequence up to 3 is not good.
Because this result is same to the next dia.
Black 1 is a gote end game but, white 2 makes black 1 sente end game.
White 2 is also important.
If white 1, black can capture the corner, and whites are seperated each other.
The sequence up to here is the basic jeongseok sequence of avalnche.