(;AB[er][lr][mr][bq][cq][dq][fq][gq][jq][kq][mq][bp][dp][kp][mp][eo][ko][mo][fn][hn][jn][qn][em][jm][qk]AW[kr][eq][lq][oq][cp][ep][fp][gp][hp][jp][lp][qp][bo][co][do][jo][lo][oo][kn][ln][mn][nn][dm][dl]C[White plays.

Source:
    Tesuji Dictionary, by Segoe Kensaku & Go Seigen]SZ[19]

(;W[jr]C[A good looking move, but a mistake in timing.];B[iq];W[hq]C[White has a splitting attack between the 2 stones on the left and the 5 stones on the right.  White seems to be heading for a live group.];B[ir];W[hr];B[ks]C[Black saves the stones on the right, but ...];W[fr]C[... White captures 2 stones.];B[dr]C[Unfortunately, White's capture only produces 1 eye.  White dies!])
(;W[fr]C[Correct timing.]
(;B[dr]C[Defending the corner gives White an extra move to help the center bottom stones.];W[jr];B[iq];W[ir]C[Now White can push from this side to capture more than 2 stones and live.];B[hq];W[gr]C[White wins the semeai.])
(;B[gr]C[Defending from the other side also fails.];W[jr];B[iq];W[hq];B[ir];W[hr]C[White still has a splitting attack, but ...];B[ks];W[gs]C[... this time White captures 3 stones.];B[dr];W[gq]C[And White saves all but a couple of the bottom center stones.])))