(;GM[1]FF[4]SZ[19]AP[SmartGo:2.5.0.0]CA[utf-8]
GN[TowerProblemSOLUTION]
RU[Simple]
AB[ab:cb][hb][cc][fc:gc][bd][ce][fe][df:ef]
AW[ba:ca][db:de][fb][cd]
PL[W]
C[This is the go problem on the lobby wall in the Hangzhou Tian Yuan Tower in Hangzhou, China, where this year’s World Amateur Go Championship was held. According to our guide on a tour there, “it’s impossible to solve this problem.” See how you can do!
]
;W[be];B[cf];W[ad]LB[ac:A][bc:B]
C[The best result for Black is the ko at A; it looks like Black can win by resisting more strongly with the connection at B, but...

See the variation for the solution.]
(;B[ac])
(;B[bc];W[bf];B[bg];W[ae];B[ag];W[da];B[af];W[aa];B[ac];W[be]
C[“Far from impossible,” notes John Fairbairn, “especially once you know the name of the problem, Shenlong Guotu, or Divine Dragon Shedding Its Skin. The Daoist phrase ‘shedding bones,’ or variants such as ‘shedding a skin’, always signify it's an under-the-stones problem,” says Fairbairn, a longtime go writer and co-author of the Games of Go on Disk encyclopedia.]
))

