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

Difference game]
PL[B]

AB[pa][bb][cb][db][ob][cc][oc][pc][bd][cd][pd][be][oe][qe][qf][rf]
AW[da][eb][pb][qb][sb][dc][ec][qc][dd][qd][rd][ce][ee][re][bf][cf]

;B[sf]C[B1]MN[1]
;W[qa]C[W2]MN[2]
;B[af]C[B3]MN[3]
;W[oa]C[W4]MN[4]

;
)
