Longest Mate Problem

The task record for a legal position is this one: Petrovici, "Problem", 1969

White Mates in 270 moves

|[ ][=][ ][=][ ][=][ ][=]|
|[B][k][=][ ][=][p][=][p]|
|[ ][P][ ][=][ ][p][ ][=]|
|[K][P][=][ ][n][ ][=][p]|
|[ ][P][ ][p][ ][=][ ][=]|
|[=][P][p][ ][=][p][=][ ]|
|[B][=][P][=][ ][=][ ][=]|
|[=][ ][=][ ][=][ ][=][B]|


1.Bb1 h4 2.Ka4 Ka8
(Black's king oscillates to and from b7 except when a black pawn is moved)

3.Ka3 4.Ka2 5.Ka1 6.Ba2 7.Kb1 8.Kc1 9.Kd1 10.Ke1 11.Bb1 12.Kf1
(White begins a triangulation in order to lose the move)

13.Kf2 14.Ke1 15.Kd1 15.Kc1 17.Ba2 18.Kb1 19.Ka1 20.Bb1 21.Ka2 22.Ka3 23.Ka4 Kb7 24.Ka5 f5
(Black moves a pawn rather than permit White's king to be moved to a6. White makes nine more triangulations, each time forcing Black to move a pawn)

47...pf4 70...pf6 93...pf5 116...ph3 139...ph2 162...ph6 185...ph5 208...ph4 231...ph3, and now

254.Ka5 Kc8 255.Ka6 f2 256.b7+ Kd7 257 b8=Q f1=Q 258.Q:e5 Q:h1 259.Qg7+ Ke6 260.Qg6+ Ke5 261.Bb8+ Ke4 262.Qc6+ Ke3 263.Q:h1 Kf2 264.B:f4 Ke2 265.b6 d3 266.c:d3 Kf2 267.Bc2 Ke2 268.Bd1+ Kf2 269.Qf3+ Kg1 270.Be3 mate.

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