(;
AB[sb][ib][rc][qc][pc][jc][od][nd][md][ld][kd]
AW[ra][oa][rb][qb][pb][lb][mc][lc]
C[Black plays.  (professional level problem)

Source:  Jimmy Cha 4p,
"American GO Journal", Fall 1989.
But appeared without a solution!

Perhaps somewhat jokingly, Jimmy Cha said a 6-dan
amateur would need 5 years to solve this problem.];

B[ma]
(;
W[na]
(;
B[la];
W[kb]C[Forced]
(;
B[ja];
W[ka];
B[nb];
W[nc];
B[ob];
W[oc];
B[pa]
(;
W[mb];
B[oa];
W[na];
B[ma];
W[la];
B[sc];
W[na]C[The last half dozen moves or so are forced.];
B[sa];
W[qa];
B[ob]
C[Simple.
Pros aren't so tough.]
)
    (;
    W[oa]C[Fails quicker than the main line.];
    B[jb]
    )
)
    (;
    B[nb]C[Fails.  Black cannot transpose O18 for K19!];
    W[nc]
    (;
    B[ja]C[Immediate transpose fails.];
    W[oc];
    B[ka];
    W[mb]
    )
        (;
        B[ob];
        W[oc];
        B[pa];
        W[oa]
        C[White is no longer short of liberties without
the B-K19, W-L19 exchange.]
        )
    )
)
    (;
    B[ob]C[Fails];
    W[nb];
    B[oc];
    W[pa];
    B[la];
    W[kb];
    B[ka];
    W[ja]
    )
    (;
    B[nb]C[Fails];
    W[nc];
    B[ob];
    W[oc];
    B[pa];
    W[oa];
    B[na];
    W[la];
    B[sc];
    W[mb];
    B[oa];
    W[qa];
    B[oa];
    W[na]
    )
)
    (;
    W[la];
    B[ob];
    W[nb];
    B[oc]
    )
    (;
    W[nb];
    B[la];
    W[kb];
    B[ka]
    )
    (;
    W[mb];
    B[ob]
    )
)
