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 "U.S. Championship"]
[Site "?"]
[Date "2012.??.??"]
[Round "?"]
[White "GM Gata Kamsky"]
[Black "GM Alexander Onischuk"]
[Result "1-0"]
[BlackElo "0"]
[FEN "4Rn1k/p3bQ2/4P3/3q4/3p4/6BP/1r4PK/8 w - - 0 1"]
[SetUp "1"]
[TimeControl "0"]
[WhiteElo "0"]
1. Rxf8+ Bxf8 2. Qxf8+ Kh7 3. Qf7+ Kh8 ( { Black dare not try: } 3... Kh6 4. Bf4+ Qg5 5. Qf6+ Kh7 6. Qxg5 { White wins with a large material advantage. } ) 4. Qe8+ Kg7 5. Qd7+ Qxd7 6. exd7 { The pawn will promote. } 1-0