(;
AB[pd][qk][rm][qn][nn][mo][np][op][pq][cn][cq][cp][bm][dn][fq][em]
AW[rn][ro][qp][qq][no][mp][lp][jp][dp][eq][fp][en][dm][cm]
TR[bm]
PL[W]
C[White's response to the marked play?

Source:
    American Go Journal, Vol. 33, No. 3, p. 19
    Jujo Jiang 9P  vs.  Rui NaiWei 9P
    North American Masters tournament]
(;
W[el]
C[In the game, Rui Naiwei 9P made the innocent looking move order mistake of the atari here.];
B[fm];W[fn];B[dl];W[cl];B[dk];W[ck]
LB[cj:A]
C[White would like to extend to A instead, but that move obviously isn't possible here.  The variation shows how White could have avoided the following painful sequence for White.];
B[cj]
C[Now Black can press down here.];
W[dj];B[ek];W[bj];B[ci];W[bl];B[al];W[bk];B[ej];W[bn];B[bo];W[am];B[bi];W[ak];B[ao];W[an]
C[White has to make small life, while Black makes center thickness in sente.

Later in the game, this bad left side result causes White problems.  Black goes on to win this game.]
)
    (;
    W[bl]
    C[White could have avoided the result in the previous variation from the game, by making this atari first.

The difference seems small, but the effect here is large.];
    B[bn];W[el]
    C[Now White can come back here to atari.];
    B[fm];W[fn];B[gm];W[gq];B[dl];W[cl];B[dk]
    C[Now when Black ataris and extends here, ...];
    W[cj]
    C[... White can make the one space jump.];
    B[dj];W[ci];B[di];W[ch]
    C[With White being able to run out ahead here, you can compare that the difference with the game line is huge.]
    )
)

