Well, at least I found it surprising...

Click Here To Show Diagram Code

[go]$$Bc Black to play in the corner
$$ | . . . . . . . .
$$ | . . . . . . . .
$$ | . X X . . . . .
$$ | . . . X . . . .
$$ | . O O X O . . .
$$ | . O X O . O . .
$$ | . X X O . . . .
$$ | . . X X O O . .
$$ | . . . O . . . .
$$ +----------------[/go]

Source: https://www.101weiqi.com/q/165737/ , which says it came from the book "Lee Chang-ho’s Endgame Skills".

Just interested in what is your surprise...

I'm not sure I fully understand the problem, but is your surprise that the correct answer given by the website looks like it could generate a lot of ko treats for white - possibly something black might want to consider if another ko elsewhere on the board seems likely?

Are you supposed to play B1 to force black to throw in and thus you get to create an eye patch

_________________
North Lecale

Indeed - another possibility, and a Frequently Asked Question in my experience.

At first glance I was expecting some kind of capturing race squeeze, and was trying to figure out which of A3, A2 or B1 would minimise the damage. At first glance, the solution move leaves black with three liberties against white's four. I'm surprised that not only does black not lose the capturing race this way, but in fact you can make actual territory in the corner and don't need to remove the white stones from the board.

If Black plays C1, will White really simply reply E1?...Or will White leave the bad aji hanging of playing A3 later?

for example:

Click Here To Show Diagram Code

[go]$$Bc Black to play in the corner
$$ | . . . . . . . .
$$ | . . . . . . . .
$$ | . X X . . . . .
$$ | . . . X . . . .
$$ | 8 O O X O . . .
$$ | 7 O X O . O . .
$$ | 2 X X O . . . .
$$ | 3 . X X O O . .
$$ | . 4 1 O 5 6 . .
$$ +----------------[/go]

Ah, now you're surprised too :-)

White is dead in double ko, right?

If B chooses that option...

But this is potentially quite a negative result for Black? If there's a ko on another part of the board, white has an infinite set of ko threats? Or if white is losing, white could potentially force a triple ko to avoid a loss? Black can avoid this by capturing the white stones and taking them off the board, but this takes a couple of moves and costs points.

Is this risk really worth a couple of extra points in the corner?

I think I know this one. The surprising move is

A3 certainly looks like a vital point. I wonder if B can just play it immediately.

_________________
A good system naturally covers all corner cases without further effort.

Click Here To Show Diagram Code

[go]$$Bc Black to play in the corner
$$ | . . . . . . . .
$$ | . . . . . . . .
$$ | . X X . . . . .
$$ | . . 7 X . . . .
$$ | . O O X O . . .
$$ | . O X O . O . .
$$ | 1 X X O . . . .
$$ | 4 . X X O O . .
$$ | . 2 3 O 5 6 . .
$$ +----------------[/go]

Click Here To Show Diagram Code

[go]$$Bc Black to play in the corner
$$ | . . . . . . . .
$$ | . . . . . . . .
$$ | . X X . . . . .
$$ | . 7 3 X . . . .
$$ | . O O X O . . .
$$ | . O X O . O . .
$$ | 1 X X O . . . .
$$ | 2 . X X O O . .
$$ | . 5 4 O 6 . . .
$$ +----------------[/go]

A3 seems to work - even if white tries to resist?

Click Here To Show Diagram Code

[go]$$Bc Black to play in the corner
$$ | . . . . . . . .
$$ | . . . . . . . .
$$ | . X X . . . . .
$$ | . . . X . . . .
$$ | . O O X O . . .
$$ | . O X O . O . .
$$ | 1 X X O . . . .
$$ | 5 . X X O O . .
$$ | . 3 2 O 4 . . .
$$ +----------------[/go]

Possible outcome?