(;
AB[nb][nc][ob][mc][md][me][mf][mg][od][pe][of][ng][nh][rg][rh][oh][ph][qh]
AW[pb][pc][oc][nd][qd][rf]
C[Pro Pair Go Tsumego 1 (Answer)

Michael Redmond 9P is graciously providing all E-Journal readers with a set of tsumego problems featured at the 2016 pro pair go tournament.  Of course, these problems are quite tough, but nevertheless entertaining to everyone, especially because Michael will later provide each solution.

In this tsumego contest, each pair has up to 10 minutes to answer each problem, but only the first 5 pairs can answer.  The race to answer first makes these problems highly challenging.  After signalling having an answer, a pair must play each move within 5 seconds.  The pair team plays Black's moves, while the composer plays White's, which allows the composers to show their favorite variation for White.

Michael gives this interesting background for this tsumego from Ohashi Hirofumi 6P:

"This problem is misleading, in that Black's first and 3rd moves are relatively easy to find, while White 4 is counter-intuitive.  Ohashi tells me that he saw surprise and maybe shock in the top Chinese pairs faces when he played move 4, but Ke Jie quickly recovered, flickering his fingers in a burst of concentration, and was in time to give the correct answer."]
(;
B[rd]
C[Correct first move.]
(;
W[rc]
C[This is easy to kill, and is not White's best response.];
B[re];W[qe];B[qf];W[sd];B[sf]
C[Dead.]
)
    (;
    W[qe];B[re];W[qf]
    (;
    B[rc];W[se];B[qb];W[pa];B[sb];W[ra];B[sd]
    C[Dead.]
    )
        (;
        B[sf]
        LB[rc:A]
        C[It is easier for Black to kill by playing this move at A, instead.];
        W[se]
        C[This may look like White can live with a squeeze, but actually Black has a good move now.];
        B[rb]
        (;
        W[sg];B[qb];W[pa];B[qc];W[pd];B[sc]
        C[White is dead.]
        )
            (;
            W[qb];B[sd];W[rc];B[sb]
            C[Dead.]
            )
            (;
            W[rc];B[qb];W[qa];B[ra];W[pa];B[qc];W[pd];B[sc]
            C[White is dead.]
            )
        )
    )
    (;
    W[re]
    C[White's strongest response.]
    (;
    B[rb]
    C[Black's correct play.]
    (;
    W[qb];B[rc];W[qe];B[sb]
    C[The vital point.  Now this will be a nakade, or if White tries to widen the space, Black can win the semeai.]
    (;
    W[ra];B[pa]
    (;
    W[sd];B[sf];W[se];B[sc];W[pd];B[oa];W[qa];B[qc]
    C[Dead with the 'flower six' shape.]
    )
        (;
        W[sf];B[sd];W[qc];B[qf]
        C[Black wins the semeai.]
        )
    )
        (;
        W[pa];B[ra];W[sd];B[qf]
        C[Black wins the semeai.]
        )
    )
        (;
        W[rc];B[qb]
        (;
        W[qa];B[ra];W[pa];B[qc]
        C[Dead.]
        )
            (;
            W[sd];B[qc]
            C[Dead.]
            )
        )
        (;
        W[qa]
        C[This is the variation that even pros found tricky.  The mistake leading to a ko is immediately seen, and the correct answer looks like it might be a seki, but...]
        (;
        B[qc]
        C[Mistake.];
        W[rc]
        (;
        B[qb];W[sb]
        C[This will be a ko.]
        )
            (;
            B[sc];W[qb];B[rc];W[ra];B[qe];W[pd];B[sb];W[sf]
            C[This will be a ko.]
            )
        )
            (;
            B[rc];W[qe];B[sb]
            C[This is still the vital point, and ...];
            W[ra]
            (;
            B[oa]
            C[This is the killing move.  If White tries to capture the Black stones, it will be a nakade, and if White protects at A, Black wins the semeai.]
            (;
            W[sd];B[pa];W[qb];B[sf];W[se];B[sc];W[pd];B[qc]
            C[Dead.]
            )
                (;
                W[pa];B[sd]
                C[Black wins the semeai.]
                )
            )
                (;
                B[sd]
                C[Mistake.];
                W[se];B[qf];W[qc];B[pd];W[qb]
                C[White wins the semeai.]
                )
            )
        )
    )
        (;
        B[qb]
        C[Mistake.];
        W[rb];B[ra];W[rc];B[pa];W[sd]
        C[Alive.]
        )
        (;
        B[rc]
        C[Mistake.];
        W[rb];B[ra];W[qb]
        C[Alive.]
        )
    )
)
    (;
    B[rb]
    C[This may look like a vital point, but does not work in this case.  White has a number of ways to make ko, which is a failure for Black.  I will show one variation.];
    W[rc];B[qb];W[pa];B[rd]
    C[This move is the tesuji, but White can get a ko.];
    W[sb];B[qc];W[ra];B[sc];W[qa]
    C[Ko.]
    )
    (;
    B[rc]
    C[Mistake.];
    W[rb]
    (;
    B[rd];W[re]
    C[Alive.]
    )
        (;
        B[sb];W[qc];B[ra];W[qb];B[re];W[rd];B[sd];W[qe];B[sf];W[sc]
        C[Alive with double ko.]
        )
    )
)

