(;
AB[oj][ni][oh][og][of][oe][od][oc][ob][oa][pc][rc][rh][rk][qk][pk][pj]
AW[rb][rd][qd][pd][pe][qg][pi][qi][qj]
C[Pro Pair Go Tsumego 6 (Answer)

Presented here is the answer to the 6th (and last) tsumego from Michael Redmond 9P's coverage of the challenging tsumego problems featured at the 2016 pro pair go tournament.

The author of this tsumego is Kono Rin 9P.];
B[qc]
C[Correct first move.  Anywhere else, and White would live by playing here.];
W[ri]
TR[rh]
C[White 2 is also forced.  Any other move and Black would just save the marked stone.  Why did Kono Rin 9P start this tsumego with two obvious moves? The White stone in the corner has an important role to play later in the variations, so maybe Kono felt that the original position was a more natural looking way to have it on the board.]
(;
B[sj];W[si]
C[The 3-4 exchange has the effect of reducing White's liberties.];
B[qf];W[pf];B[qh]
(;
W[ph];B[pg];W[rg]
(;
B[rf];W[sh];B[sf];W[sc];B[oi];W[re];B[rj];W[se];B[rh];W[sb];B[ra];W[qb];B[qa]
C[Dead.  Temporarily, this might look like a seki, but while White cannot do anything, it is possible for Black to fill liberties from the corner and capture the White group.]
)
    (;
    B[re]
    C[Mistake.];
    W[se];B[sf];W[sc]
    C[Ko is bad for Black.]
    )
)
    (;
    W[rg];B[rf];W[ph];B[pg];W[sh];B[sf]
    (;
    W[sc];B[oi];W[re];B[rj];W[se];B[rh];W[sb];B[ra];W[qb];B[qa]
    C[Dead.  Temporarily, this might look like a seki, but while White cannot do anything, it is possible for Black to fill liberties from the corner and capture the White group.]
    )
        (;
        W[se];B[sc];W[re];B[sd]
        C[Dead.]
        )
    )
)
    (;
    B[qf]
    C[Mistake.];
    W[pf];B[qh];W[ph];B[pg];W[rg]
    (;
    B[rf];W[sh]
    (;
    B[sf]
    TR[rb];
    W[sc];B[sj];W[re];B[si];W[se];B[rh];W[qh];B[rj];W[sg]
    C[Alive.  Black lost the semeai by only one move.  This variation has a direct connection to the correct answer, which is an improvement in the order of moves.  Even most pros will read this out first, and then use this failed variation as a hint to find the correct answer.]
    )
        (;
        B[se];W[sd];B[sc];W[sf]
        C[Ko is not good enough for Black.]
        )
    )
        (;
        B[re]
        TR[rb]
        C[Without the marked White stone, this would finish White off, but...]
        (;
        W[se];B[sf];W[sc]
        TR[rb]
        C[White gets a ko with the help of the marked stone.  Ko is not good enough for Black.]
        )
            (;
            W[sd]
            C[White's mistake.];
            B[sf];W[sh];B[sc];W[rf];B[se]
            C[Dead.]
            )
        )
    )
    (;
    B[re]
    C[Mistake.];
    W[se];B[sf];W[sc]
    TR[rb]
    C[The marked White stone helps to let White make a ko.  Ko is not good enough for Black.]
    )
)

