(;GM[1]FF[4]CA[UTF-8]AP[CGoban:2]ST[2]
RU[Japanese]SZ[19]KM[0.00]TM[]
PW[White]PB[Black]AW[bb][cb][db][ac][bc][dc][dd][de][df]AB[ba][eb][gb][fc][ad][cd][ed][gd][be][ce][ff][bg][cg][dg][eg]LB[ba:1]C[black played 1. how to respond?]PL[W]
(;W[aa]CR[aa]
;B[ab]CR[ab]
(;W[ca]CR[ca]C[RIGHT
black cannot connect: no ko])
(;W[da]CR[da]
;B[aa]CR[aa]))
(;W[ca]CR[ca]
;B[aa]CR[aa])
(;W[da]CR[da]
;B[aa]CR[aa])
(;W[bd]CR[bd]
;B[aa]CR[aa])
(;W[cc]CR[cc]
;B[aa]CR[aa])
(;W[ec]CR[ec]
;B[aa]CR[aa]
;W[ee]CR[ee]
;B[fd]CR[fd]
;W[fe]CR[fe]
;B[ge]CR[ge]))