(;
AB[oi][oh][nh][mh][mg][oj][lg][lf][le][lc][lb][rh][nb][oa][pa][qb][qa][ra][sb][sc][sd][se][rf][rg][na][qh][qi][qj][pj][mb]
AW[qf][og][ng][mf][me][md][od][ob][pb][mc][sf][qg][rb][rc][rd][re]
C[Pro Pair Go Tsumego 5 (Answer)

Presented here is the answer to the 5th 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 Ohashi Hirofumi 6P.

Michael adds some clarifications about the multiple correct variations for this problem:
"Despite what I said in my comments about tsumego 3, in this 5th tsumego White has a number of choices for variations to get a direct ko.  There are differences such as size of territory when White lives, and whether Black gets to play the outside connection in the process, which would be important in an actual game, but not in a tsumego.  Such an abundance of correct variations is generally considered a flaw, but in my opinion the high level of difficulty and the beauty of some of the variations makes it a worthy tsumego anyway.  I must add that all the choices are for White several moves into the correct answer, and since Black has only one correct sequence, by the strict rules of tsumego it is a valid problem."]
(;
B[pg]
C[Correct];
W[pf];B[pd]
C[Black's first move (forcing White 2) has reduced White's eye space.];
W[qc]
(;
B[oe]
C[Black's correct move.White has three possible moves, all will end in a ko.]
(;
W[pc];B[qe]
(;
W[of]
C[White's correct move.];
B[nd];W[nc];B[oc];W[sa];B[ld]
C[Ko is the correct answer.]
)
    (;
    W[ne]
    C[Mistake];
    B[of];W[ph];B[nc]
    (;
    W[nf];B[oc]
    C[Dead]
    )
        (;
        W[sa];B[oc];W[nd];B[ld]
        C[Dead.]
        )
    )
)
    (;
    W[oc];B[qe]
    (;
    W[ph]
    C[Correct move for White.];
    B[pe]
    C[Two variations, both will be a ko.]
    (;
    W[of]
    C[This will be a ko];
    B[nc];W[nd];B[pi];W[sa];B[sb];W[pc];B[pg]
    LB[nf:A][ph:B][ne:C]
    C[Ko is the answer. If White connects at A, this group will die. If White takes once at B and then plays at C, the group is alive.]
    )
        (;
        W[nf];B[nc];W[nd]
        (;
        B[sg]
        C[Black's mistake.];
        W[pc];B[pi];W[pg]
        C[Alive with seki]
        )
            (;
            B[pc]
            C[Mistake.];
            W[sa]
            C[Alive.]
            )
            (;
            B[pi]
            C[Ko is the correct answer. White must win this ko to make a seki. Since this might not be obvious, I will add two continuations for White.]
            (;
            W[pg]
            C[Mistake.];
            B[pc];W[sa];B[ld];W[qd]
            C[Since the center is a temporary seki and White's side is dead, the whole group will die.]
            )
                (;
                W[pc];B[pg]
                LB[of:A][ph:B]
                C[Ko is the correct answer. If White connects at A, this will die. If White wins and connects the ko at B, White will be alive with seki.]
                )
            )
        )
    )
        (;
        W[of]
        C[Mistake];
        B[nc];W[nd];B[ph];W[nf];B[pe];W[sa];B[sb]
        C[Dead]
        )
    )
    (;
    W[of];B[qe]
    (;
    W[pc]
    C[White's correct move.];
    B[nd];W[nc];B[oc];W[sa];B[ld]
    LB[od:A][nf:B][ph:C]
    C[Ko (at A) is the correct answer. If White connects at B, Black will play at C.]
    )
        (;
        W[oc]
        C[White's mistake];
        B[nc];W[nd];B[ph];W[nf];B[pe];W[sa];B[sb]
        C[Dead.]
        )
    )
)
    (;
    B[pc]
    C[Mistake. This looks easy, but actually Black has fallen into a trap.];
    W[oc];B[qe]
    (;
    W[oe]
    C[This will live.]
    (;
    B[nf];W[sa]
    C[Alive.]
    )
        (;
        B[qd];W[nf]
        C[Alive]
        )
    )
        (;
        W[nf]
        C[This will live.]
        (;
        B[pe];W[ph];B[oe];W[sa];B[nc];W[nd]
        C[Alive]
        )
            (;
            B[qd];W[oe]
            C[Alive]
            )
        )
        (;
        W[sa]
        C[White's mistake.];
        B[of];W[ph];B[pe];W[pg];B[nf]
        C[Dead]
        )
    )
)
    (;
    B[pd]
    C[This tsuke is a tesuji, but is wrong as the first move.];
    W[pe];B[qc];W[of];B[pg];W[ne]
    C[Alive]
    )
    (;
    B[pe]
    C[Wrong]
    (;
    W[pd]
    C[Now White will live.];
    B[qe];W[oe];B[pg];W[of];B[pf];W[nc];B[pc];W[ne]
    C[Alive]
    )
        (;
        W[qe]
        C[White's mistake Now the group will die.];
        B[pd];W[qc];B[nf];W[of];B[oe]
        (;
        W[ne];B[pc];W[oc];B[nc];W[nd];B[ld];W[nf];B[pg]
        C[Dead.]
        )
            (;
            W[pc];B[nc];W[nd];B[oc];W[ne];B[ld];W[nf];B[pg]
            C[Dead.]
            )
        )
    )
    (;
    B[qc]
    C[Wrong];
    W[pe];B[pd];W[of]
    C[White is alive.]
    )
    (;
    B[pc]
    C[Wrong];
    W[pe];B[pg];W[of];B[ne];W[qc];B[oc];W[pd]
    C[Alive]
    )
)

