(;GM[1]FF[4]CA[UTF-8]AP[CGoban:3]ST[2]
RU[Japanese]SZ[19]KM[0.50]
GN[ ]PW[White]PB[Black]WR[14k]BR[14k]DT[2010-09-28]GC[Black to play]AW[bp][cp][dp][aq][eq][fq][br][fr]AB[bq][cq][dq][cr][er][ds][es]C[Our starting point.]FG[259:]PM[0]
;B[]C[It's white's turn.]
(;W[cc]C[The main line, which ends as scenario 6, will ultimately turn out to show black's  best line of play.  White knows he can win the ko, so he takes a 10 point move.  The variation, scenario 1, shows white killing the corner right away.]
(;B[ar]LB[qq:A]C[Black understands (or has heard somewhere) that this move, a tesuji for getting a ko in the corner, is mysteriously better than taking a ten point move at A.  The variation on this move shows scenario 2, which is what happens when black never starts the ko.]
(;W[as]C[White must take, or else he loses a sum greater than anything else on the board.  The variation on this move, scenario 3, shows this happening.]
(;B[bs]C[Black starts the ko.  This is a ko move and we assume that it is worth 11 points.  This has something to do with the fact that if black wins the ko and lives in the corner, he might expand from this position, and the 11 points are somehow an average of whether he does or doesn't live.  For my purposes, I think it suffices to say that it is worth more than 10 points.
 The variation on this move, scenario 4,  shows what happens when he changes his mind about following up his tesuji.]
(;W[cs]C[White must take.  If he doesn't, he will lose out just as in scenario 3.  The variationon this  move, scenario 5, shows this happening.]
;B[qq]C[Black takes a ten point move]
;AE[bq][cq][dq][cr]AW[fd][ee][df][dr]AB[pn][oo][np]LB[fd:F][ee:D][df:B][pn:E][oo:C][np:A]TR[cc]SQ[qq]C[End of Scenario 6.  White kills black.  Black is just as dead as in scenario 1, 2 or 4, but gets to play A which white answers with B etc.  The rest of the game is played out with black and white exchanging moves of diminishing value.  Black has effectively cancelled out all of the profit white has made elsewhere.   When we compare this to scenario 1, we see that the result is virtually identical.  When we compare it to scenario 2 or 4 however, where Black didn't play the ko, we see that black's squared move has cancelled out white's triangled move, and he is thus better off.  ])
(;W[dd]C[Scenario 5. As in scenario 3, white needlessly lets black win the ko.]
;AE[br][as]AW[fd][ee][df]AB[qo][pp][oq][ar]LB[fd:E][ee:C][df:A][qo:F][pp:D][oq:B]TR[cc][dd]C[End of scenario 5.   Although white profits from the triangled stones, they are worth less than the profit black has made by winning the ko and living in the corner.   A - F effectively cancel each other out. This scenario is not viable for white.]))
(;B[np]LB[np:A]TR[cc]C[Scenario 4.  Black plays elsewhere at A, thinking erroneously that this move is worth more than starting the ko.]
;AW[fd][ee][df]AB[pn][oo]LB[fd:F][ee:D][df:B][pn:E][oo:C][np:A]TR[cc]C[End of scenario 4.  White need not play in the corner, and so an exchange of moves A-F etc ensues.  These moves effectively cancel each other out, and at the end of the game, white has not given anything up to kill the corner, and has made the profit of the triangled stone.]))
(;W[dd]C[Scenario 3, white lets b win the ko.]
;AE[br]AW[fd][ee][df]AB[pn][oo][np][bs]LB[fd:E][ee:C][df:A][pn:F][oo:D][np:B]TR[cc][dd]C[End of scenario 3.   Although white profits from the triangled stones, they are worth less than the profit black has made by winning the ko and living in the corner.   A - F effectively cancel each other out. This scenario is not viable for white.]))
(;B[np]LB[np:A]C[Scenario 2.  Black sees the ko as unwinnable, and so he takes a 10 point move elsewhere.]
;AW[fd][ee][df]AB[pn][oo]LB[fd:F][ee:D][df:B][pn:E][oo:C][np:A][ar:1]TR[cc]C[End of scenario 2.  The rest of the game is played out with black and white exchanging moves of diminishing value.   Black is dead in the corner without white having had to play at 1.   In this scenario, at the end of the game, the triangled move is white's profit.  ]))
(;W[ar]C[Scenario 1:  White kills black right away.]
;AW[cc][dd][ee]AB[oo][pp][qq]LB[cc:B][dd:D][ee:F][oo:E][pp:C][qq:A]C[End of scenario 1.
Black and white exchange moves of diminishing value which effectively cancel each other out.   I do not see why this is worse for white than scenario 6, except that white has given black a few opportunities to make a mistake.]))