Half the variations which are calculated in a tournament game turn out to be completely superfluous. Unfortunately, no one knows in advance which half.
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[Event "rated untimed match"]
[Site "?"]
[Date "????.??.??"]
[Round "?"]
[White "Bogoljubov"]
[Black "Erdelyi"]
[Result "1-0"]
[Annotator "David Hayes"]
[BlackElo "0"]
[FEN "3rk3/1R5p/8/4Pp2/5Pp1/2bp2P1/r2B3P/3RK3 b - - 0 1"]
[SetUp "1"]
[TimeControl "0"]
[WhiteElo "0"]
1... Rxd2 2. Rxd2 Ra8 3. Rb1 ( { An interesting line that leads to surprising
mate. } 3. Rb2 Ra1+ 4. Kf2 Bd4+ 5. Kg2 Rg1# ) 3... Ra2 4. Rd1 { Black can continue
to improve his position while white is in zugzwang. } 4... Ke7 5. Kf2 Rxd2+ 6. Rxd2 Bxd2 { Black wins with a large material advantage. } 1-0