David2009: Dgebuadze vs Fedorov, 2006 The notorious NN vs P ending! The final position is clearly drawn, but did Black miss a winning chance at move 48? 
click for larger view48...Na6! blockades the a Pawn on a5 to leave Black with the difficult task of shepherding his united passed Pawns to promotion. White can use his own passed h Pawn to win one of them, but the remaining Pawns seems to cost Black his N to leave K+Pa5 versus KNN which may or may not be a difficult win for the NN pair. One possible continuation (not necessarily best for either side) is 48...Nba6 49.Nd2 Kf6 50.h4 Kg6 51.Nf3 f6 52.Ke7 e5 53.Ng1 f5 54.h5+ Kxh5 55.Kf6 Kg4 56.Kxe5 f4 57.Kd4 Kg3 
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The Ns exert a powerful cramping influence on White's King, and Black will have to surrender his N to prevent the Pawn promotion. Black's moves are my idea, White's moves are found by setting up Crafty End Game Trainer in a colours-reversed link: http://www.chessvideos.tv/endgame-t...
with initial position (the coloured-reverse version of the first diagram) 
click for larger view From the second diagram, the game might continue
58.Ne2+ Kf3 59.Nc3 Kf2 60.Nd1+ Ke1 61.Ne3 fxe3 62.Kxe3 to reach
click for larger viewThere is now a table-base mate in 90 but I don't know whether or not White with best defence can force a draw by the 50 move rule. In the longest variation White takes refuge in the h8 corner, Black then lifts the blockade temporarily to coax the a5 Pawn forward one square so re-starting the 50-move clock. If White doesn't oblige by moving the Pawn, the second N has just time to mate him in the h8 corner. The Pawn is then blockaded on a6, White is winkled out of the h8 corner, is driven towards the 'a' file and is finally mated in the a1 corner. At present, my best guess is that White can just manage to force a 50-move draw by not moving his Pawn during the first part of the process. Here's a further link to Crafty End Game Trainer to win the colours-reversed ending:
click for larger view Colours-reversed NN vs P ending: link http://www.chessvideos.tv/endgame-t... Against Crafty EGT the win is not too difficult because the EGT makes the mistake of heading towards its own Pawn. A sterner challenge is had by playing against "Endgamebot" (thanks, <Ludens>!) on the Free Internet Chess Server (FICS), using the command "tell endgamebot play FEN-string" where 'FEN-string" is the FEN string corresponding to the desired position. I intend to put further analysis of this ending on my forum. | 
