❤ PUZZLES: A tsumego a day keeps the doctor away

[Lys]

I don’t know.

It was more than two years ago:

Doubt about tsumego

Hi there! I’m trying some Cho Chikun’s tsumego. This one I really can’t understand. It says: “Black to kill” (I turned off all options, so it’s top left corner and black to move I couldn’t find an answer, so I tried to click everywhere and found a sequence that says “Correct”. But still I can’t understand why white should be dead… it looks like seki to me. I would not spoiler this puzzle, but don’t know how to discuss the solutiion otherwise. Any thought?