From a game between a 3k and 4k on KGS.
Following , Black is dead.
HermanHiddema: Terrible result, of course
Black lives, but having played 15 stones, he has gained 4 points of territory and is completely sealed into the corner. Perhaps better to die than to live this way.
HermanHiddema: should be at a to prevent white from connecting under. If white defends at b, black plays at and loses nothing. If white starts the ko, black takes first and can always fall back to after white retakes. White doesn't need to play in this diagram, playing at kills the black group. Therefore, should be at .
HermanHiddema: is a mistake, it should be at . After black is sealed in.
Velobici: Then this might be an example of two kyu level mistakes: joseki moves mistakenly transposed one line and not taking into account stones on the board () that are absent in the joseki. In other words, were at the corner star point, and would start the attach and block joseki. In that joseki is not present and Black plays a after .
Andy: I also agree that should be at . Black won't go far wrong if he remembers that it is almost never favourable (when starting from a mostly even position) to make life in the corner at the expense of getting shut out of the rest of the board. That being said, in the diagram, if it's going to be played, has to be played with the intention of creating cutting points in the white shape. After white properly forces with giving black bad shape and then covers one of the cutting points with , black must cut immediately at the remaining cutting point x. Black's group is alive in the corner, so he can (and should) fight in the center very aggressively. Black can look forward to a pincering attack on whichever side white doesn't defend (since she can't defend both at the same time). It looks to me like whatever happens that is going to wind up feeling misplaced giving black a larger corner than he deserves and giving white an inefficient shape on the left.
HermanHiddema: is risky, If black plays at he may still escape his confinement. White could play a to simply make shape or play at to force black to walk on the second line.
HermanHiddema: should be at to create cutting points, now you've only put a weak stone to close to a strong white formation. is a little strange, playing a is sufficient.