(;
C[Dan Game
Commentary:  Yuan Zhou 7d
Game editors:  Bill Cobb, Myron Souris
Published in the September 1, 2020 edition of the American Go E-Journal.

In this dan level game with no komi, Yuan Zhou gives practical and easy to understand examples for planning for a ko, using thickness, and playing useful sente plays.

Yuan Zhou 7 dan is one of the strongest players in the US.  He has won many titles.  Zhou is also a popular teacher, lecturer, and author.  He lives in Germantown, MD, and can be reached at yuan.zhou@zhouyuan.com .  This commentary is typical for Zhou, who has published several books, including such thorough commentaries of pro games at Slate & Shell (www.slateandshell.com).];
W[dc];B[cp];W[pq]
C[Fine.  Nothing wrong here.];
B[qo];W[ep]
C[All fine still.];
B[eq]
C[A valid choice.];
W[fq];B[dq]
C[Still nothing wrong.  Go Seigen says this situation in the lower left is already a gain for White.]
(;
W[fp];B[op]
LB[cn:A]
C[This game move is playable, but normally, Black responds with A instead.  Pressing down here, Black wants sente to play at A. ]
(;
W[co]
LB[oq:A]
C[Locally, White's move is a good follow-up.  The problem is that Black A is a huge move, so White should try to get sente on the left in order to prevent Black A.];
B[bo];W[bn]
C[This hane is a good choice for White to get sente.];
B[do];W[cn];B[dp];W[em]
C[White's jump here is not sente - Black's corner is already alive.

Instead, White should return to the lower right.];
B[fn]
C[Cutting off White first is a good idea.];
W[en];B[eo];W[fo]
TR[fn]
LB[oq:A]
C[The marked stone's ladder is good for White, while Black wants to return to the bottom right with A.];
B[bp]
C[But Black is worried about this corner.  This move is sente, because of the push and cut threat.];
W[cl]
C[So White protects.];
B[gn]
C[And Black is also able to get this move in.];
W[hp]
C[White must respond locally.];
B[oq]
C[Finally returning to the lower right here, Black makes a huge gain.  This opening is good for Black.  White's 5 stone group to the left is not that thick.];
W[in]
C[White needs to attack the 2 stones.];
B[gl]
(;
W[or]
C[White aims to make a ko, but this idea is not good - too early in the game.];
B[nr]
C[Good for Black.];
W[qr];B[os];W[ps];B[pr]
C[Dangerous for White - this ko is very big.  Black could get a huge corner with great thickness.  The gain for Black would be 30+ points.];
W[er]
C[Dangerous.  Is this move really a ko threat?]
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B[dr]
C[The variation shows a better way.];
W[or]
C[Finding a ko threat now is hard for Black.  Capturing the ko will be pretty big for White.];
B[ns]
C[Given the situation, connecting here is the right decision for Black.];
W[pr]
C[This corner result is worse for White than what we saw in an earlier variation.];
B[no]
C[The correct move - fixing the cutting points.];
W[mq]
C[Peeping here is correct.];
B[nq];W[rp]
C[White's play here makes the corner alive.]
(;
B[jp]
LB[qp:A]
C[Locally, the correct move to attack, threatening a cut.  But see the variation.];
W[jq]
LB[ro:A][kq:B][jr:C]
C[A good defense.  Now Black should play the seal at A and then attack White's group on the left side.

Black could also hane at B, let White descend to C, and then attack on the left side.];
B[iq]
C[Black tries to fight too hard here.];
W[ip];B[kq];W[jr]
TR[mq]
C[Black's attack is the wrong idea.  White's marked stone helps White.];
B[ir]
C[Black seems to have misread here.];
W[kr];B[lr];W[kp];B[jo]
C[Black realizes that playing in the center is more important.];
W[lq];B[io]
C[Black seems to have misread here again.];
W[ho];B[hn];W[jn]
C[Misreading this ladder, Black loses his early lead.  White is better now.];
B[ro];W[qp];B[pp];W[so]
C[This hane is unnecessary, and doesn't help White.];
B[sn];W[ko]
C[Capturing here is a big mistake.  Although this move does have value by preventing Black from making ladder breaker moves.];
B[rq]
C[Shows good reading.  White loses this corner.];
W[sq];B[sr]
C[White's corner is dead.  Black is good in the game again.];
W[gj]
LB[di:A]
C[White should play at A, instead.  White is so thick at the bottom that Black would still have to run.];
B[fk]
C[White is driving Black toward his unsettled group on the left side.];
W[ei];B[dk];W[bj]
C[White is not in good shape here.]
(;
B[il]
C[The wrong direction.  Black fails to take advantage.];
W[hk];B[hl]
C[White now can make perfect use of his thickness.];
W[kk]
C[Even though Black can run out, White obtains lots of free moves in the center.];
B[fj];W[fi];B[jk];W[kj]
C[White is doing well, keeping Black struggling.];
B[kl];W[ll]
C[White makes perfect use of the thickness below.];
B[jj];W[ji];B[ii]
C[The game actually continues for 100 more moves, but Black is fighting in a hostile environment.  Black finally resigns when White kills too many more stones.  White's advantage of his thickness in the lower center was insurmountable.];
W[ij];B[hi];W[ik];B[jl];W[gi];B[lm];W[ml];B[mm];W[nl];B[jh];W[ki];B[kn];W[ih];B[ce];W[cd];B[de];W[fd];B[ck];W[bk];B[ch];W[cj];B[fe];W[ge];B[bd];W[bc];B[ff];W[gf];B[dg];W[nc];B[qf];W[ne];B[gd];W[fc];B[pb];W[ob];B[oc];W[nb];B[dd];W[cc];B[hd];W[ie];B[md];W[nd];B[jc];W[id];B[ic];W[hb];B[ke];W[jf];B[hc];W[gb];B[lf];W[mg];B[mf];W[nf];B[lg];W[lc];B[mh];W[ng];B[jg];W[ig];B[lh];W[oi];B[hh];W[gg];B[mj];W[ni];B[lj];W[lk];B[ok];W[nj];B[nk];W[mk];B[ol];W[nm];B[nn];W[om];B[pm];W[hg];B[kh];W[gh];B[kf];W[ld];B[jd];W[he];B[nh];W[oh];B[og];W[pg];B[on];W[hj];B[of];W[pf];B[oe];W[pe];B[od];W[qd];B[pc];W[qc];B[qb];W[rb]
C[Black resigns here.]
)
    (;
    B[ck];W[bk];B[di]
    C[Black breaks the seal.];
    W[ej];B[dl]
    LB[cm:A]
    C[White has to respond.  Otherwise, Black ataris at A to kill 2 stones.  So Black can get out here.

Black does not want to get out in front of White's thickness in the lower center, as in the game.]
    )
)
    (;
    B[qp]
    C[Black should play here.];
    W[rq];B[ro]
    C[Big sente plays for Black.];
    W[rs];B[jp]
    C[Now Black can play here for sente.];
    W[jq];B[kq]
    C[Black can take these 2 sente plays, and then ...];
    W[iq];B[cj]
    C[... attack on the left side.  This attack is pretty big actually.]
    )
)
    (;
    B[qs]
    C[Black should end the ko here.  The following shows why Black's left corner is safe.];
    W[dr];B[cr];W[br];B[bs];W[bq]
    C[Another ko, but Black has already gained in the lower right.];
    B[ar];W[aq];B[cq];W[as];B[fr]
    C[White cannot win this ko - Black has too many local ko threats.]
    )
)
    (;
    W[il]
    C[White should continue with this jump.];
    B[gj];W[di]
    C[This normal continuation is good for White.

If Black gets to play where White just played here on the left side, White's lower left group could come under attack.

And White still has aji in the lower right corner.  See the next variation.]
    )
    (;
    W[kq]
    C[To show the aji in the lower right corner, assume that White has already played here on the bottom side.];
    W[pp]
    C[Now White can push up.];
    B[po];W[or]
    C[Sente.];
    B[nr];W[pr];B[mq]
    C[Black has to protect against a cut here.];
    W[qp]
    TR[kq]
    C[White's corner is now alive, thanks to the marked stone.]
    )
)
    (;
    W[oq];B[np];W[mq]
    C[This pattern is common with AI programs.  This result is not a loss for White.];
    B[cn]
    C[Black can now extend here, which is good, but ...];
    W[mp]
    C[... White can now push up here.  In effect, White has gotten a bigger area at the bottom than with a normal extension from the 3 stones on the left.

Not needing to extend at the bottom is a gain for White.  Black has gained in the lower right, but White has gained at the bottom.  So this result is fine for White.]
    )
)
    (;
    W[qm]
    C[White can pincer here.];
    B[oo];W[np];B[pl];W[qp];B[ql];W[ro];B[qn];W[rn];B[rm];W[fp]
    C[Now White connects.];
    B[cn];W[jq]
    LB[op:A]
    C[You will find this pattern in pro game records.  White has prevented Black's sente play at A.]
    )
)

