(;GM[1]FF[4]SZ[19]
GN[Answer]
PC[http://senseis.xmp.net/?L2Group/Discussion]AP[GoWiki:2009]
DT[2009-04-22]
C[Diagram from http://senseis.xmp.net/?L2Group/Discussion

Answer]
PL[B]

AB[ca][ab][cb][db][cc][bd][cd][be]
AW[ba][da][bb][eb][dc][ec][dd][ce][ee][bf][cf]
LB[ad:a]

;B[ae]C[B1]MN[1]
;W[ac]C[W2]MN[2]
;B[bc]C[B3]MN[3]
;W[aa]C[W4]MN[4]

;LB[ad:a]
)
