(;GM[1]FF[4]CA[UTF-8]AP[CGoban:3]ST[2]
RU[Japanese]SZ[13]KM[0.00]
AW[fa][ja][fb][jb][fc][jc][dd][ed][jd][de][ke][df][kf][dg][ig][jg][kg][dh][ih][ci][di][fi][gi][hi][cj][dj][ej][ck][dk][ek]AB[ea][ka][eb][kb][cc][dc][ec][kc][cd][kd][ld][ce][je][le][cf][lf][cg][lg][bh][ch][hh][jh][kh][lh][bi][ii][ji][bj][fj][gj][hj][bk][fk][bl][cl][dl][el][fl]C[The following problem is adapted from a recent game of mine. 

This is an extract from a 19x19 game, and not a complete 13x13 board position.

It is Black to play. White could have played a defensive 
move
 to fix the bad
 aji as the dame were being filled, 
but then he
 would have lost 
by half a point (the game was
played under
 Japanese rules). Therefore 
any gain
counts as a success 
for Black: capturing some stones, 
seki or 
ko.

This problem is rather difficult: you probably need to be a
high 
dan player to solve it in your head. However, I suggest
that 
you try for a while, and then explore variations on a board
before 
looking at the answers: there are many beautiful
tesujis, snapbacks, 
and connect-and-dies hidden within as
rewards for the determined 
traveller.

A few hints:
1) Add a second stone and sacrifice both.
2) My solution relied on the dango in the lower left not being 
an eye, but someone else found another solution that works regardless.

Incidentally, this demonstrates an aspect of Japanese rules I 
prefer over AGA. It is much more satisfying for a game to be 
decided by a problem like this than the randomness of dame parity.])
