Vision:
It's magari shimoku, white cannot move, because his group of stones will then be eaten, and black simply waits until the end of the game, when there are no co-threats left and eat the white group

TNTErick:
SGF

TNTErick:
To those who are unsure about the answer, or think it is wrong: The solution is a special case of both 3-in-5 seki and bent-4 on-the-corner. You may think that the solution gives a 3-in-5 Seki shape, but things are a little bit more complicated than that. You see that the opponent could not do anything like a normal seki (the second longest chains if you check my .sgf file), this holds true even if you stretch and complete the outer shell (5th move in the longest chain), but things are a little bit more complicated than that. Now you can atari from the inside (7th move in the longest chain) to make it a bent-4 on-the-corner, where you can kill the opponent in this sector if you win a ko. This is why some may argue that you need a fight of Ko to kill them. You may guess what I'm going to say now... "Things are a little bit more complicated than that." We know that the opponent can do nothing in here, so we can turn this pseudo-Seki into a Ko fight WHENEVER we want. Imagine you're actually playing the entire go game, and you turn these three stones into a ko fight AFTER the whole game is finished. Well, there are no Ko-threats since they are finished off during the endgame, so you do win this ko fight as long as the outer shell of this section is not killed. That is why it says "no Ko/no Seki" on the title though it looks like it has a Ko in it. And that is why the solution here is considered better than straight up Hane-ing it into a bent-4 on-the-corner. By doing it, you are putting yourself into an unnecessary Ko fight.

ALROCHARARI:
Ko is here needed to win no?

Neal Wright:
@clackie this is bent four in the corner therefore white is dead

clackie:
The solution is clearly seki