Have fun with some blunders here.
 Number 1
A group with an eye wins a capturing race against a group without an eye but loses it against a group with two eyes. was definitely a mistake here. White had some possibilities for ko too, but some persistence... -- HolIgor
The problem here seems to be that White wants it all. Instead of trying to defend two stones, which are not directly relevant for the capturing race, White should just start reducing Black's liberties straight away. Black will capture the stones but arrive too late to save the corner.
White can of course choose to play the ko (after ), but it is probably not favourable.
Black can try this to kill White. If White misreads the position, playing is suicidal. (White can resist with at , but Black a, White b at 1 and Black c wins the semeai.)
But of course, White should not respond to with , but play at and make the group live. Black will then play a to make two eyes for the black group in gote. Similarly, if Black plays at , White should respond at , and will win the capturing race. -- Morten Pahle (10k)
Bill: This is a complex and difficult position, with different options for ko, seki, and independent life. Proper play depends upon the rest of the board, not only the ko threat situation, but the sizes of other plays. I think I know correct play when neither player has a ko threat and the other plays on the board are of moderate size.
is the vital point, I believe.
Earlier, threatens to make two eyes. - makes a two stage ko.
 Number 2
Strange thing but happened in one of my games recently. I was so glad. The correct move is to capture at a. -- HolIgor
 Number 3
This happens quite often with weaker players. Black decides to save the marked stone and plays . White continues with , so becomes a totally wasted move. Correct moves are at a or depending on the situation. Then Black has sente in this corner. -- HolIgor
 Number 4
 Number 5
Robert Pauli: I'd say there is no ko. W has no problems to capture.
 Number 6
... and when I played , he said "Wow!". and are wrong moves, I guess you can figure out why yourself. :)
Black-2 at solves this problem. As I see it, White cannot kill any stones here without help from Black. ---PokaMyoshu
 Number 7
I've seen this happen often with beginners, and done it myself a couple of times too. White just played , and Black went at . If were one point to the left, would have been good. -- Bisqwit
 Number 8: Fool's Seki
Looking through some of my old games I've found this funny ko threat. HolIgor