tderz: What could happen in these 2 positions?
Ed?: White seems beyond reasonable hope. 2 and 3 or 'a' and 'b' seem to be miai. White can probably dig up an unreasonable approach ko.
tderz: If at b, it reverts to some variations below, if black cuts at . c and a are miai now. at a would allow white to live in a favourable ko.
When I gave my friend a comment on the position at game move 173 (some moves earlier) - I asked him what the possible outcomes could be theoretically, but without calculating, just at a glance.
Especially cases iii) and iv) have to be avoided.
In the game, not this position, Black has many more liberties (ok, that's calculating now), so any approach ko with 3 or more necessary moves is usually considered worth very little.
at c, W-d?, eye (W dead) is tempting, but white will resist with ko: , , Bc, ->d.
Ed?: White is in trouble as black has 'a' or 'b'
tderz: I wanted to see espec. .
tderz: -> with miai of eyes , is equivalent.
This is the local seki -> center group dead -> huge win. (in the game)
Ed?: This is the best I have found for white. White has a ko but needs two approach moves ( one at 'a' and one at 'b').
tderz: What if black does not play , but tenuki?
I have the feeling that black cannot improve his position now, by playing (he cannot approach either) - a ko should be taken last.
White can use 3 moves to approach at a, e and b, Black had to take the the direct ko at - and keep it that way (very dangerous).
Perhaps black could play after the approach move a only.
But the position is clearly won if Black gives White no chance to make the ko real. So perhaps is safest.
Just lost a tournament game involving a 2-3-stage ko which I did not take serious (but my game losing oversight was somewhere else).