(;
AB[fm][eo][ep][cp][fq][iq][er]
AW[cl][cn][dn][dp][dq][cr]
C[What is Black's best endgame play?

Source:
"Tesuji Problems"
Go World #26, p. 22,  Winter 1981]
(;
B[br]
C[Correct.  This contact play is easy to overlook in the heat of a game.]
(;
W[cq]
C[Connecting is unreasonable.];
B[cs];W[ds];B[bs];W[dr];B[bq];W[do]
C[Inevitably, White has to connect.];
B[bo];W[bn];B[ao]
C[Black lives in the corner, which is a disaster for White.]
)
    (;
    W[bq]
    C[Because of the previous variation, White must give way here.];
    B[cs]
    (;
    W[ar];B[dr]
    C[A clever follow-up.];
    W[cq]
    C[White cannot allow Black to atari here, so White must connect.];
    B[do];W[co];B[bs]
    C[Black makes a big corner reduction.

Even worse, eventually White will have to add another stone inside White's territory.]
    )
        (;
        W[ds]
        C[Starting a ko is unreasonable.];
        B[dr];W[bs]
        C[For example ...];
        B[cq]
        C[A picnic ko for Black.]
        )
    )
)
    (;
    B[do]
    C[The ordinary sequence, starting with this push, has little effect on White's corner.];
    W[co]
    (;
    B[dr];W[cq];B[cs];W[bs];B[ds];W[bq]
    )
        (;
        B[br];W[bq]
        )
    )
)

