(;GM[1]FF[4]SZ[19]
GN[2-1 is __often__ but not __always__ vital]
PC[http://senseis.xmp.net/?BeginnerExercise83/Solution]AP[GoWiki:2009]
DT[2009-04-22]
C[Diagram from http://senseis.xmp.net/?BeginnerExercise83/Solution

2-1 is __often__ but not __always__ vital]
PL[W]

AB[cn][bo][ap][cp][dp][dq][fq][er]
AW[bp][bq][cq][dr][cs]
CR[ap]
LB[ds:a]

;W[ar]C[W1]MN[1]
;B[bs]C[B2]MN[2]
;W[br]C[W3]MN[3]
;B[es]C[B4]MN[4]

;CR[ap]
LB[ds:a]
)
