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Wikipedia's article on the fifty-move rule states:

In the 20th century it was discovered that some positions of certain endgames can only be won in more than fifty moves (without a capture or a pawn move). The rule was changed to include certain exceptions in which one hundred moves were allowed with particular material combinations. However, more and more exceptions were discovered and in 1992 FIDE abolished all such exceptions and reinstated the strict fifty-move rule.

I have never seen an example of this, though I used to think the K, N, B vs. K ending was one. When is it possible to force a win in 50 moves or more, but not less than 50 moves?

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up vote 8 down vote accepted

Yes, there are quite a few endgames that require more than 50 moves with best play from the defender.

Wikipedia has a list of material imbalances where it could take more than 50 moves depending on the specific position. Here are a few examples:

  • Rook and bishop vs lone rook (often a draw though)
  • Two bishops vs a lone knight
  • Two knights vs a lone pawn (the defender must have a pawn)
  • Four knights vs a lone queen (would never happen over the board…)
  • Queen and rook vs queen and rook
  • Two queens vs two queens
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Wow... I see that 517 moves to force a win has even bee proven! That's amazing! –  Daniel May 2 '12 at 20:33
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