Joseki-related life-and-death example 1
This is a common 4-4 point enclosure joseki.
can also be played at a. In fact, it is the most common reply in professional games.
can also be played at b.
ends the joseki.
The group in the corner is alive, as discussed in L+2 group.
The atari at is a mistake. After , white is caught in a shortage of liberties and is unable to play at a.
However, the descent at a is sente.
I'll comment that, because Black's threatened ko is indirect, one cannot assume it is really sente until the latter stages of the game. This may affect fighting on the outside.
 Note however that it is usually an endgame mistake to play the descent. Instead, Black should start at b.
Bildstein: That's very interesting. Can anyone explain why?
tderz: White will have about 5-6 points. (depending on the timing of the n-m-p exchange).
Black ends in sente.
tderz: White will have about 4-1=3 points or less (depending on the timing of the n-m-p exchange).
Black ends in gote.
Conclusion: starting with b in dia. seems to be about 2 points better for Black, and it seems to me that Black is relatively free to chose when to play, because White has no sente variation herself for improvement.
I hope that no errors crept in.