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What is the longest (currently discovered) number of moves for a forced mate position where players will use both the 50-move draw rule and the 3-fold repetition rule if it will help them avoid losing.

Edit: Where the losing player attempts to make the game last as long as possible (or if possible draw) and the winning player attempts to checkmate as fast as possible. Both players playing perfectly.

For those interested this question covers where the 50-move rule is ignored: What endgame has the longest known forced checkmate?

  • Do you mean the longest shortest forced mate? (that is, white doesn't waste time but always plays the move that forces the quickest mate)? In that case 3-fold repetition would never occur. – RemcoGerlich Jun 5 '18 at 7:31
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    Yes, longest forced mate where the losing player attempts to make the game last as long as possible and the winning player attempts to checkmate as fast as possible. Both players playing perfectly. – silent-tiger Jun 5 '18 at 7:42
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    @Steve but ending databases CAN play perfectly, and so can computers as long as the move tree can stay small enough, so it is definitely possible to have a puzzle position that involves perfect play. – Guy Schalnat Jun 5 '18 at 14:56
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    @Steve So what you have been asserting all this time is that something the question does not ask for is not possible? – James Hollis Jun 5 '18 at 15:50
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    @steve Sure, I understand that chess is unsolved and likely unsolvable (also perhaps a draw?). My thoughts were more along the lines that you have checkmate in 1,2,3,4 etc positions. Whats the largest one of them that has currently been discovered where the draw rules are in effect. – silent-tiger Jun 6 '18 at 1:29
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Otto Blathy is famous for his long mate problems. There are different records depending on whether you allow an illegal starting position, or promoted pieces, or minor duals in the solution, so your answer might be anywhere between 257 and 292 moves.

This answer on Puzzling.SE shows you a construction in 270 moves:

     [Title "Otto Blathy - White to play and mate in 270"]
 [FEN "8/Bk3p1p/1P3p2/KP2n2p/1P1p4/1Pp2p2/B1P5/7B w - - 0 1"]

(legal position, with promoted piece, with minor duals in the solution)

Those problems involve regular pawn moves, so the fifty-moves rule doesn't change their validity. On the other hand, all long (500+ moves) tablebase mates (as the first diagram in the answer linked above) show series of more than 50 moves without capture nor pawn moves.

Finally a beautiful problem exploiting the 50-moves rule was composed by Noam Elkies, who comes sometimes on Chess.SE. I will refrain from giving the solution here for people who want to search (but I have already given away the main indication and lazy people can just follow the link).

     [Title "Noam Elkies, 1991 - White to play and draw"]
 [FEN "8/1p6/1p6/kPp2P1K/2P5/N1Pp4/q2P4/1N6 w - - 0 1"]

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