Black resigned after seeing the marked move. What will happen if black keeps playing? A very good practice for some deep reading.
A hint:
The marked stone helps a ladder.
$$W
$$ +---------------------------------------+
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | X O O O . . . . . . . . O O . . . . . |
$$ | . X O X . . O . X . . X X X O O O . . |
$$ | X X X O O O . . . , . X O O . X O X . |
$$ | . X O . O . . . . . X O . O . . X O . |
$$ | . X X O O X X . X X O . O X . X O O . |
$$ | . X O O X X O . . . O . O O . X O . . |
$$ | . O X X O . . X . X . O X O O O X X . |
$$ | . O . X . O . . . . X . X X X X O O . |
$$ | . O X , . . . . . O X . . . . , X O . |
$$ | . O X . . . . . . . O . . . . . . . . |
$$ | . X . @ . . . . . X . . . . . . . . . |
$$ | . . . . . . . . X O O . X . . X . . . |
$$ | . X . . . . . . . X . O . O X . X . . |
$$ | O X X X . . . . O X . O . O O X X . . |
$$ | . O O , X . X X . X X X X X O O X . . |
$$ | O . O O O . O . . X O X O O . O X . . |
$$ | X O . . . . O X X O . O O . O X . X . |
$$ | . . . . . . . . . . O . . O . . X . . |
$$ +---------------------------------------+
[go]$$W
$$ +---------------------------------------+
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | X O O O . . . . . . . . O O . . . . . |
$$ | . X O X . . O . X . . X X X O O O . . |
$$ | X X X O O O . . . , . X O O . X O X . |
$$ | . X O . O . . . . . X O . O . . X O . |
$$ | . X X O O X X . X X O . O X . X O O . |
$$ | . X O O X X O . . . O . O O . X O . . |
$$ | . O X X O . . X . X . O X O O O X X . |
$$ | . O . X . O . . . . X . X X X X O O . |
$$ | . O X , . . . . . O X . . . . , X O . |
$$ | . O X . . . . . . . O . . . . . . . . |
$$ | . X . @ . . . . . X . . . . . . . . . |
$$ | . . . . . . . . X O O . X . . X . . . |
$$ | . X . . . . . . . X . O . O X . X . . |
$$ | O X X X . . . . O X . O . O O X X . . |
$$ | . O O , X . X X . X X X X X O O X . . |
$$ | O . O O O . O . . X O X O O . O X . . |
$$ | X O . . . . O X X O . O O . O X . X . |
$$ | . . . . . . . . . . O . . O . . X . . |
$$ +---------------------------------------+[/go]
Yeah, I was surprised when I saw that on wbaduk, here is what I found:
$$B
$$ +---------------------------------------+
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | X O O O . . . . . . . . O O . . . . . |
$$ | . X O X . . O . X . . X X X O O O . . |
$$ | X X X O O O . . . , . X O O . X O X . |
$$ | . X O . O . . . . . X O . O . . X O . |
$$ | . X X O O X X . X X O . O X . X O O . |
$$ | . X O O X X O . . . O . O O . X O . . |
$$ | . O X X O . . X . X . O X O O O X X . |
$$ | . O . X . O . . . . X . X X X X O O . |
$$ | . O X , . . . . 9 O X . . . . , X O . |
$$ | . O X . . . . 8 3 5 O . . . . . . . . |
$$ | . X 1 @ . . . 4 2 X . . . . . . . . . |
$$ | . . . . . . . . X O O . X . . X . . . |
$$ | . X . . . . . . 0 X . O . O X . X . . |
$$ | O X X X . 6 . . O X . O . O O X X . . |
$$ | . O O , X 7 X X . X X X X X O O X . . |
$$ | O . O O O . O . . X O X O O . O X . . |
$$ | X O . . . . O X X O . O O . O X . X . |
$$ | . . . . . . . . . . O . . O . . X . . |
$$ +---------------------------------------+
[go]$$B
$$ +---------------------------------------+
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | X O O O . . . . . . . . O O . . . . . |
$$ | . X O X . . O . X . . X X X O O O . . |
$$ | X X X O O O . . . , . X O O . X O X . |
$$ | . X O . O . . . . . X O . O . . X O . |
$$ | . X X O O X X . X X O . O X . X O O . |
$$ | . X O O X X O . . . O . O O . X O . . |
$$ | . O X X O . . X . X . O X O O O X X . |
$$ | . O . X . O . . . . X . X X X X O O . |
$$ | . O X , . . . . 9 O X . . . . , X O . |
$$ | . O X . . . . 8 3 5 O . . . . . . . . |
$$ | . X 1 @ . . . 4 2 X . . . . . . . . . |
$$ | . . . . . . . . X O O . X . . X . . . |
$$ | . X . . . . . . 0 X . O . O X . X . . |
$$ | O X X X . 6 . . O X . O . O O X X . . |
$$ | . O O , X 7 X X . X X X X X O O X . . |
$$ | O . O O O . O . . X O X O O . O X . . |
$$ | X O . . . . O X X O . O O . O X . X . |
$$ | . . . . . . . . . . O . . O . . X . . |
$$ +---------------------------------------+[/go]
(Maybe 6 should be before 2 so that you lose less if black compromises)
$$B
$$ +---------------------------------------+
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | X O O O . . . . . . . . O O . . . . . |
$$ | . X O X . . O . X . . X X X O O O . . |
$$ | X X X O O O . . . , . X O O . X O X . |
$$ | . X O . O . . . . . X O . O . . X O . |
$$ | . X X O O X X . X X O . O X . X O O . |
$$ | . X O O X X O . . . O . O O . X O . . |
$$ | . O X X O . . X . X . O X O O O X X . |
$$ | . O . X . O . . . . X . X X X X O O . |
$$ | . O X , . . . . X O X . . . . , X O . |
$$ | . O X . . . . O X X O . . . . . . . . |
$$ | . X X O . 0 . O O X . . . . . . . . . |
$$ | . . . . . 9 2 1 X O O . X . . X . . . |
$$ | . X . . 8 7 5 3 O X . O . O X . X . . |
$$ | O X X X . O 6 4 O X . O . O O X X . . |
$$ | . O O , X X X X . X X X X X O O X . . |
$$ | O . O O O . O . . X O X O O . O X . . |
$$ | X O . . . . O X X O . O O . O X . X . |
$$ | . . . . . . . . . . O . . O . . X . . |
$$ +---------------------------------------+
[go]$$B
$$ +---------------------------------------+
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | X O O O . . . . . . . . O O . . . . . |
$$ | . X O X . . O . X . . X X X O O O . . |
$$ | X X X O O O . . . , . X O O . X O X . |
$$ | . X O . O . . . . . X O . O . . X O . |
$$ | . X X O O X X . X X O . O X . X O O . |
$$ | . X O O X X O . . . O . O O . X O . . |
$$ | . O X X O . . X . X . O X O O O X X . |
$$ | . O . X . O . . . . X . X X X X O O . |
$$ | . O X , . . . . X O X . . . . , X O . |
$$ | . O X . . . . O X X O . . . . . . . . |
$$ | . X X O . 0 . O O X . . . . . . . . . |
$$ | . . . . . 9 2 1 X O O . X . . X . . . |
$$ | . X . . 8 7 5 3 O X . O . O X . X . . |
$$ | O X X X . O 6 4 O X . O . O O X X . . |
$$ | . O O , X X X X . X X X X X O O X . . |
$$ | O . O O O . O . . X O X O O . O X . . |
$$ | X O . . . . O X X O . O O . O X . X . |
$$ | . . . . . . . . . . O . . O . . X . . |
$$ +---------------------------------------+[/go]
$$B
$$ +---------------------------------------+
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | X O O O . . . . . . . . O O . . . . . |
$$ | . X O X . . O . X . . X X X O O O . . |
$$ | X X X O O O . . . , . X O O . X O X . |
$$ | . X O . O . . . . . X O . O . . X O . |
$$ | . X X O O X X . X X O . O X . X O O . |
$$ | . X O O X X O . . . O . O O . X O . . |
$$ | . O X X O . . X . X . O X O O O X X . |
$$ | . O . X . O . . . . X . X X X X O O . |
$$ | . O X , . . . . X O X . . . . , X O . |
$$ | . O X . . . . O X X O . . . . . . . . |
$$ | . X X O 4 O 3 O O X . . . . . . . . . |
$$ | . . . 2 1 X O X X O O . X . . X . . . |
$$ | . X . . O X X X O X . O . O X . X . . |
$$ | O X X X . O O O O X . O . O O X X . . |
$$ | . O O , X X X X . X X X X X O O X . . |
$$ | O . O O O . O . . X O X O O . O X . . |
$$ | X O . . . . O X X O . O O . O X . X . |
$$ | . . . . . . . . . . O . . O . . X . . |
$$ +---------------------------------------+
[go]$$B
$$ +---------------------------------------+
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | X O O O . . . . . . . . O O . . . . . |
$$ | . X O X . . O . X . . X X X O O O . . |
$$ | X X X O O O . . . , . X O O . X O X . |
$$ | . X O . O . . . . . X O . O . . X O . |
$$ | . X X O O X X . X X O . O X . X O O . |
$$ | . X O O X X O . . . O . O O . X O . . |
$$ | . O X X O . . X . X . O X O O O X X . |
$$ | . O . X . O . . . . X . X X X X O O . |
$$ | . O X , . . . . X O X . . . . , X O . |
$$ | . O X . . . . O X X O . . . . . . . . |
$$ | . X X O 4 O 3 O O X . . . . . . . . . |
$$ | . . . 2 1 X O X X O O . X . . X . . . |
$$ | . X . . O X X X O X . O . O X . X . . |
$$ | O X X X . O O O O X . O . O O X X . . |
$$ | . O O , X X X X . X X X X X O O X . . |
$$ | O . O O O . O . . X O X O O . O X . . |
$$ | X O . . . . O X X O . O O . O X . X . |
$$ | . . . . . . . . . . O . . O . . X . . |
$$ +---------------------------------------+[/go]
However I didn't check if black had a way other than simple connect to answer the first peep that would simultaneously fix the ladder, but then white may be able to find a move to resurrect the miai. But that sequence looks like the main line white is aiming at.