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Master Class Vol.10: Mikhail Botvinnik
Our experts show, using the games of Botvinnik, how to employ specific openings successfully, which model strategies are present in specific structures, how to find tactical solutions and rules for how to bring endings to a successful conclusion
This was a very complicated riddle that also touched the rules of chess. Charles Sullivan had immediately pointed out White has many ways to reach a won position but in many lines he fails to mate the enemy king in 50 moves or less which means that Black can draw according to the 50-move-rule.
But what was Bronstein's last and decisive mistake? Was it 52...Nc8?, a move that loses with and without the 50-move- rule, whereas 52...Ne7 draws as Jan Timman had shown earlier.
Many lines in the analysis of this endgame lead to endgames with two bishops against knight, which are theoretically won but not with 50-move-rule.
This leads to a question related to chess history: which version of the 50-move-rule was used in 1951? Nowadays, FIDE decrees that the 50-move-rule always applies, with no exception and no matter whether certain positions will lead to mate in a given number of moves. However, in the past the rule was applied differently. Fortunately, Harold van der Heijden was able to shed some light on this issue. He writes:
"The ending was considered a draw from 1851 (Horwitz & Kling fortress) until the 1980’s when Thompson and Comay independently used a computer to prove that the ending is a general win.
Then about the rules.
In a book that is pretty close to the 1951 date of the game, André Chéron (Lille, 1952): Nouveau Traité Complet D’Échecs – La Fin de Partie, dedicates a chapter (page 741) to 50 move plus endings ("Les Finales Exigeant Plus de 50 Coups"). He mentions BR vs R, 2N vs P and R + Pa2 vs B (black squares) + Pa3. Of course, he does NOT mention 2B vs. N but for a certain limited and clearly defined number of positions, he proposes to change the 50-move-rule, and to allow the side which makes winning attempts 100 moves in which no pawn is moved and no piece or pawn is taken before the game is declared drawn.
So it seems that Chéron PROPOSES a new rule in 1952 …. which indicates that such exceptions did not exist?"
Thus, Charles Sullivan and Zoran Petronijevic had to work very hard to prove not only that White could win but also to prove that White can win within the limits of the 50-move-rule.
After burning a lot of midnight oil Zoran Petronijevic reached the following conclusions:
Here's the complete analysis of this difficult and historically important ending.