(;
AB[is][fs][ir][er][br][iq][aq][hp][bp][go][eo][do][co][bn]
AW[gs][gr][cr][gq][fq][eq][dq][cq][bq]
PL[W]
C[White plays.

Source:
   Xuan Xuan QiJing, classic 14th century problem set]
(;
W[ar];B[as]
(;
W[es]
C[White's 1st two moves can be in either order.];
B[ds]
(;
W[bs]
C[White's 3rd throw-in in a row!];
B[cs]
(;
W[fr]
(;
B[dr]
LB[ap:A][ar:B]
C[Unfavorable 2 step ko for Black.  Best sequence for both sides.

Black has to connect A and B to win the ko.]
)
    (;
    B[es]
    C[Even worse.];
    W[dr];B[ap];W[bs];B[cs];W[es]
    C[White lives outright.]
    )
)
    (;
    W[dr]
    C[Bad timing.  White still has a squeeze, but ...];
    B[fr]
    C[... Black can dodge to here!];
    W[es];B[fr];W[bs];B[cs]
    C[White dies.]
    )
)
    (;
    W[fr]
    C[Inferior.];
    B[ap]
    LB[es:A]
    C[Now White only has a direct ko.  Black only needs to connect at A to win the ko.]
    )
    (;
    W[cs]
    C[Fails.];
    B[ar]
    C[Without the squeeze, White dies.]
    )
    (;
    W[dr]
    C[Fails.];
    B[ap]
    (;
    W[bs];B[ar]
    C[White dies.]
    )
        (;
        W[fr];B[es]
        C[White dies.]
        )
    )
)
    (;
    W[bs]
    C[Bad timing.];
    B[cs]
    (;
    W[es];B[fr]
    C[White dies.]
    )
        (;
        W[dr];B[es]
        C[White dies.]
        )
    )
    (;
    W[dr]
    C[Fails.];
    B[es]
    C[White has only one eye.]
    )
)
    (;
    W[bs]
    LB[cs:A]
    C[(or White A)  Fails.];
    B[ar]
    C[Black eliminates any possibility of a liberty shortage.]
    )
)

