(;GM[1]FF[4]CA[UTF-8]AP[CGoban:3]ST[2]
RU[Japanese]SZ[19]KM[6.50]
GN[Zipper Problem]PW[White]PB[Black]CP[© 2010 Fort Myers Go Club]GC[This work is licensed under the Creative Commons Attribution 3.0
United States License. To view a copy of this license, visit:
http://creativecommons.org/licenses/by/3.0/us/
or send a letter to:
Creative Commons
171 Second Street, Suite 300
San Francisco, California, 94105, USA.]SO[http://www.fortmyersgo.org/]AW[ap][bp][cq][dq][br][er][fr][ds]AB[cn][ao][bo][eo][cp][dp][gp][eq][fq][gr][fs][gs]C[Black to play.]
(;B[ar]
;W[bq]
(;B[bs]
(;W[cs]C[CHOICE]
(;B[dr]
;W[as]LB[dr:A][cs:4]TR[bs]C[Correct. This is a two-step ko. White also has a choice of seki by playing 4 at A instead if black has surplus ko threats (navigation solution).RIGHT])
(;B[es]
;W[dr]C[Wrong. White is alive.])
(;B[cr]
;W[dr]C[Wrong. White is alive.])
(;B[as]
;W[es]C[Wrong. White is alive.]))
(;W[dr]C[CHOICE]
(;B[cs]LB[dr:4][cs:A]C[Correct. This is a seki. White has also a choice of a favorable ko by playing 4 at A instead (navigate solution).RIGHT])
(;B[as]
;W[cs]C[Wrong. White is alive.])
(;B[aq]
;W[cs]C[Wrong. White is alive.])))
(;B[cs]
;W[bs]C[Wrong. White is alive.])
(;B[es]
;W[dr]C[Wrong. White is alive.])
(;B[dr]
;W[cr]
(;B[bs]
;W[es]C[Wrong. White is alive.])
(;B[es]
;W[bs]
;B[dr]
;W[er]C[Wrong. White is alive.])
(;B[cs]
;W[bs]C[Wrong. White is alive.])
(;B[as]
;W[bs]C[Wrong. White is alive.])))
(;B[dr]
;W[as]
(;B[es]
;W[cs]C[Wrong. White is alive.])
(;B[cs]
;W[cr]C[Wrong. White is alive.])
(;B[cr]
;W[cs]C[Wrong. White is alive.]))
(;B[es]
;W[as]
(;B[dr]
;W[cs]C[Wrong. White is alive.])
(;B[cs]
;W[dr]C[Wrong. White is alive.])
(;B[cr]
;W[dr]C[Wrong. White is alive.]))
(;B[cs]
;W[bs]C[Wrong. White is alive.])
(;B[cr]
;W[bs]C[Wrong. White is alive.]))