(;
AB[ja][ma][na][oa][jb][mb][pb][rb][jc][mc][pc][qc][rc][jd][md][je][oe][pe][qe][kf][sf][jg][lg][mg][pg][qg][rg][nh][qh][sh][ri]
AW[ka][kb][nb][ob][kc][sc][kd][nd][od][pd][qd][rd][sd][ke][le][ne][lf][nf][of][pf][qf][rf]
C[Black plays.

Source:
    Qi Jing Zhong Miao #494, an ancient collection of mostly kyu level life and death problems.
    This problem is a classic on a freedom race, eyes, and seki.

Analysis:
    Myron Souris]
(;
B[sb]
C[The only way.];
W[qa]
C[Forced];
B[pa]
C[Forced, but sente.];
W[ra];B[se]
C[The crucial move.  Only the relative size of the internal eyes determines the semeai winner.  White's eye now has only 3 points, Black's has 4 points.

The shared internal freedoms are more numerous than White's external freedoms.  So to win, Black only has to eliminate White's outside freedoms, fill in the internal shared freedoms, and then take advantage of his extra freedom in his larger eye.];
W[re];B[pe];W[sg];B[sf];W[qb]
C[White has to play here before the internal freedoms go away.  Might as well be now.];
B[qe];W[ld];B[sg];W[lc];B[se];W[lb];B[ng];W[la];B[og];W[nc];B[mf];W[me];B[sa]
C[With the shared internal freedoms down to 1, Black's capture purchases 3 more freedoms.];
W[qa];B[oc];W[oe]
C[But White can purchase only 2!];
B[pe]
C[So White dies!]
)
    (;
    B[se]
    C[Fails.];
    W[sb]
    C[White reduces the size of Black's eye.  Now both Black and White's eyes will each have only 1 internal freedom nearing the end of the semeai.  Because both sides share so many more internal freedoms than White's external freedoms, the result is a seki.]
    )
)

