(;GM[1]FF[4]SZ[19]
GN[Why does W4 work?]
PC[http://senseis.xmp.net/?BQM523]AP[GoWiki:2009]
DT[2010-11-07]
C[Diagram from http://senseis.xmp.net/?BQM523

Why does W4 work?]
PL[B]

AB[ec][gc][fd][de]
AW[fb][dc][fc][gd]
CR[gd]

;B[ed]C[B1]MN[1]
;W[eb]C[W2]MN[2]
;B[hc]C[B3]MN[3]
;W[dd]C[W4]MN[4]

;CR[gd]
)
