(;
AB[ps][js][qr][or][kr][ir][rq][nq][iq][gq][mp][hp][dp][no][io][in][nm][lm][jm][ol]
AW[pr][jr][pq][lq][kq][jq][rp][qp][lp][jp][ip][po][mo][lo][ko][jo][cn][qm][qk]
C[White plays.

Source:
    Tesuji Dictionary, Vol. 1, Hasami-tsuke #3
    Segoe Kensaku & Go Seigen, Ishi Press]
(;
W[nr]
C[Correct]
(;
B[ns]
C[Toughest defense.];
W[mr];B[oq];W[ms]
(;
B[ks];W[os]
LB[op:A][nn:B]
C[A ko results that is enormous for both sides, but White not only takes the ko first, but also has internal ko threats at A followed by B.]
)
    (;
    B[os]
    C[If Black avoids the ko, ...];
    W[ks]
    C[... White catches Black in a shortage of liberties.]
    )
)
    (;
    B[mr]
    C[If Black tries to avoid the ko, ...];
    W[lr];B[ks];W[ls];B[is];W[ns];B[mq];W[ms]
    C[... White makes simple forcing moves to live outright.]
    )
)
    (;
    W[lr]
    C[Fails];
    B[ks];W[ls];B[is];W[nr];B[ns]
    C[And White cannot even salvage a ko.]
    )
)

