Hello, Guo!

First of all, I hope you're doing well! Today I was playing a game and I found myself considering playing this sequence that you can see from Move 18 to Move 29 in this professional game (though in the end, I didn't play it.) When I looked it up in the database, this was the only game in which it was played. I'm puzzled by this as to me it looks like White got an acceptable local result considering that he came away with sente (if we don't consider the stone that Black already has on the top side.) So, why is this not a joseki? And can White ever play Move 18?

Thank you very much for answering this.

Have a good day.

-- bugcat

[goban sgf=https://openstudyroom.org/media/machina/attachments/Tuo_Jiaxi_-_Choi_Cheolhan.sgf move=18][/goban]