Use aji to make black live locally in the top right (r12) destroying your opponent's hopes and dreams, forcing them to resign.

Afterwards, awe in the greatness that is Yi Ch'ang-ho

Answer in the spoiler, have fun!

Well, I wouldn't exactly call it a 9p problem. I reckon any strong amateur could find it.

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Still officially AGA 5d but I play so irregularly these days that I am probably only 3d or 4d over the board (but hopefully still 5d in terms of knowledge, theory and the ability to contribute).

There is no doubt aji there and I am not a strong amateur myself but the fact that Yi read through all of that and completely rearranged the position of the game in the way he did I find it amazing.

His opponent, Yu Ch'ang-hyeok also a 9p, is no push over and I seriously doubt that a strong amateur could have seen through all of that and done what Yi did.

I rejected the game move because I assumed that W would consider cutting too dangerous and would just block and connect underneath What does B have if W declines the challenge?

Maybe a better problem is this: after the b hane, can W safely cut and capture? We have evidence that this qualifies as a 9p problem.

Agree with mitsun. I wonder, though, could it be that white chose the move that didn't work because the connection doesn't give him enough to win? The difficulty with the original situation would then lie more in positional judgement rather than reading.

Above is my guesses, I could be completely wrong. xD