OK, I misunderstood your point, because you started with …
and I thought: “wait, this isn’t really a joseki”.
But I now understand that this is irrelevant for the point you ended up making.
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Yeah it was something I edited in near the end of writing the post, and I see it doesn’t make as much sense to keep it.
I mean it basically is a “joseki”, because you don’t really lose much more than a point by the end of it, it follows the same pattern as a joseki. There’s much more disastrous results of picking a wrong “joseki” than this one.
A lot of the time the word “joseki” is used whether it’s the first corner of the game or the fourth. Its just the corner patterns that turn out even results aren’t always the same as on a near empty board.
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Spending a bit more thought on this corner situation, I’d probably play at B2 to force white B7 (making white overconcentrated), and then atari at E6 before defending at E3 (playing 2 kikashi before defending). I’d be quite happy with this result for black:
I’d even be looking to improve further on that, for example by playing black 5 at F3 or F4.
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I think it’s also fine for black, but I suppose the point would be that this and any improvement is also in gote. So there’s that trade off depending on if you wanted to approach the other 3-4, enclose a corner, take another star point etc.
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I’m not sure I understand. Is there a variation in this corner where black ends in sente?
Edit: I think I get it. You mean this:
However, I think white 2 is a mistake (an underplay) with C10 present. White shouldn’t let black end in sente so easily when white C10 is already present, even.leaving black’s forcing move at E6. I think white should at least play 2 at D7 (or E6 as you suggested, if it works).
I could be wrong though. Perhaps white 2 is the proper move, like it’s just that white made a bit dubious joseki choice earlier on and they should stay calm now and not try to recover the loss they incurred right away.
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I think white’s choice of this joseki is already a mistake. Instead of the hane at C4, white should play the hane at C1 to attack black.
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This is quite a difficult topic.
Traditional theory is that we are supposed to keep aji and not play forcing moves.
However, some forcing moves should be played, otherwise, they can’t be played in time later.
So it’s on a case-by-case basis.
Example 1:
In this typical 3-3 joseki, AI will often ask us to exchange 1 for 2 first. This may seem like a loss of ko threats, but it also makes the ko threat later in this area bigger. It will also make other forcing moves in this area more powerful since now black can’t afford to lose the 3 stones. If you just use 1 as a ko threat, it may not be big enough depending on the ko you are fighting.
Example 2:
In this flying knife joseki, AI will often ask us to complete the seki first by playing at A4 for example. This is because if you don’t play it, the opponent will play there first as a ko threat. By playing the forcing moves here, you eliminate your ko threats but you also remove your opponents ko threats. Forcing white to play C6 will make the aji at D10 more certain as well.
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Running the position by KataGo, it feels black should just defend at E3, white crawls at B2 and then black plays kikashi before defending:
White then pushes at E7 and black responds.
My suggestion of starting with black B2 loses 2 points for black (i.e., black loses their 2 point advantage).
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I’m currenty reviewing a bunch of games with ai-sensei. I realize that I sometimes miss simple forcing moves that a DDK can understand. White to play.
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what is this?!
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As a DDK representative, I don’t know.
Should I play the atari first?
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Yes, you found the move. White should play the atari first. Black needs to respond, otherwise the group H14 will die. After that, White can come back with O13.
In the game I played at O13 directly, and Black played M14 in sente since I had to protect against the double atari O15.
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Example 2 is a branch of the ridiculously complicated hypermodern flying knife joseki (also see some branches here).
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This is also a case of where the forcing move at N11 should’ve been played first if possible since it will cause black to be tight on liberties.
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Yeah I think you’re right that white 2 is a mistake, but it feels bad to tenuki if not playing E6 or D7.
It feels like black can take sente though after these, maybe answer E6 once.
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White does end in sente with KataGo’s variation (and white even gets the corner).
This is best for both according to KataGo (on low playouts).
Black is still leading by 2 points, but the cause for that is not in this diagram. It’s white’s earlier joseki choice, losing ~0.5 points with the C7 pincer, again losing ~0.5 points with the C4 inside hane, and losing 0.5 - 1.0 points with the C5 push (at least this is its assessment on low playouts).
Asking KataGo some more: black could take sente by not playing the E6 atari and capturing white’s one stone right away. KataGo feels white then needs to extend to E6, which black can ignore:
However, black’s lead is still 2 points even though they ended in sente. So KataGo seems to feel that getting E6 (with good aji = without bad aji) is worth losing sente (for both players).
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Yeah that’s an interesting one to note 
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