(;
AB[fs][br][gr][bq][gq][hq][iq][cp][dp][ip][jp][pp][fo][go][ho][cn][en][pn]
AW[ds][hr][ir][jr][cq][dq][eq][jq][nq][fp][gp][hp][kp][io][jo][ko]
C[Black plays.

Source:
     Tesuji Dictionary, by Segoe Kensaku & Go Seigen]
(;
B[dr]
C[The only move!]
(;
W[fq]
C[At first glance, White seems to catch Black in a liberty shortage.];
B[es]
C[But this 1st line tesuji connects Black's stones out to the left!];
W[fr];B[gs];W[er];B[cs];W[hs];B[ds]
)
    (;
    W[er]
    C[Blocking here also seems to give Black the lead in the semeai.  But ...];
    B[ep];W[fq];B[cr]
    C[... with the liberty shortage, White is the one who loses the semeai.]
    )
)
    (;
    B[fq]
    C[Bad timing.];
    W[ep];B[er]
    C[Otherwise, White plays here to win the semeai.];
    W[dr];B[eo];W[hs]
    C[But White wins the semeai anyway.]
    )
)

