[sgf-full](;GM[1]FF[4]CA[UTF-8]AP[CGoban:3]ST[2]
RU[Japanese]SZ[9]KM[0.00]
AW[aa][ca][ha][bb][cb][hb][ib][ac][bc][hc][dd][fd][gd][hd][id][ee][fe][cf][df][ef][eg][ch][dh][eh][fh][gh][hh][ih]AB[ga][db][fb][gb][cc][dc][ec][fc][gc][bd][cd][ed][be][ce][ge][he][ie][bf][ff][hf][bg][cg][dg][fg][gg][hg][ig][bh][bi]LB[ci:A]C[Preface - Corridors
If we want to calculate how much a move at A is worth, let us first consider a simpler case.
After reviewing the lower branches, we see that the value of a move like A increases from 0,5 as the corridor increases, but is there an upper-bound? If black plays at A, before miai consideriations, he has destroyed one potential point of white territory. Therefore, the value of this play cannot exceed one.
Therefore, the value of a corridor play like A is bound by one point and a half-point, increasing in value for a longer corridor.
/waves hand]
(;B[]LB[da:A][ea:E][ad:C][de:B][ci:D]C[Looking at the size of the moves, we see that A is worth 2p, B and E are worth 1p, and C and D are worth between 0,5p and 1p with D being slightly larger.
Therefore, if white plays first the natural sequence would be A B E D C...
So, we see that the "natural" sequence does not work. Then how should white play?
If white plays B giving black the larger move at A will his sacrifice be enough to win?]
(;W[da]C[This is a mistake by white.]
(;B[de]C[This is a mistake by black.]
;W[ea]
;B[ci]
;W[ad]LB[ae:B][di:A]C[Now, they trade corridor plays. Remember, it is black's advantage to play A instead of B since it is slightly larger.]
(;B[di]
;W[ae]
;B[ei]
;W[af]
;B[fi]
;W[ag]C[Black must respond at A2 or he will die.]
;B[ah]
;W[gi]TW[ba][ia][ab][ic][hi][ii]TB[dd][gf][if][ai]C[So, in this scenario white wins by a point.
However, what if black isn't forced to take the "lesser" point at a2, what will the result be?])
(;B[ae]
;W[di]TW[ba][ia][ab][ic][ei][fi][gi][hi][ii]TB[dd][af][gf][if][ag][ah][ai]C[White will win by a point.]))
(;B[ea]C[This move is also worth a point and now black is alive.]
;W[de]
;B[ci]
;W[ad]
(;B[di]
;W[ae]
;B[ei]
;W[af]
;B[fi]
;W[ag]
;B[gi]
;W[ah]
;B[hi]TW[ba][ia][ab][ic]TB[fa][eb][gf][if]C[This results in jigo! So, if white plays A first then black can make jigo.])
(;B[ae]
;W[di]TW[ba][ia][ab][ic][ei][fi][gi][hi][ii]TB[fa][eb][af][gf][if][ag][ah][ai]C[White will win by a point.])))
(;W[de]
;B[da]
(;W[ci]
;B[ad]TW[ba][ia][ab][ic][di][ei][fi][gi][hi][ii]TB[ea][fa][eb][ae][af][gf][if][ag][ah][ai]C[Trading D for C is not enough for white to win. This is jigo.])
(;W[ad]
(;B[ae]
;W[ci]TW[ba][ia][ab][ic][di][ei][fi][gi][hi][ii]TB[ea][fa][eb][af][gf][if][ag][ah][ai]C[Black cannot play this way, white wins by 1.])
(;B[ci]
;W[ae]
;B[di]
;W[af]
;B[ei]
;W[ag]C[Here is the crucial moment that white's play at A was look toward. Must black play a2? ]
(;B[fi]
;W[ah]
;B[ea]
;W[gi]TW[ba][ia][ab][ic][hi][ii]TB[fa][eb][gf][if]C[If he does not, he loses by 2, clearly the worst result for black thus far.])
(;B[ah]
;W[fi]TW[ba][ia][ab][ic][gi][hi][ii]TB[ea][fa][eb][gf][if][ai]C[W+1 and black could not resist. So this is the best sequence for white.])))))
(;B[ci]
(;AB[di][ei][fi][gi][hi]LB[ii:A]C[In this case, a move at A is dame and is, therefore, worth 0p.])
(;W[]
;B[di]
(;AB[ei][fi][gi]LB[hi:A]C[In this case, a move at A is worth 1p gote or 0,5p.])
(;W[]
;B[ei]
;AB[fi]LB[gi:A]C[Here, the move at A is worth 1,5p gote or 0,75p.]))))[/sgf-full]