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 "Unknown"]
[Black "Unknown86"]
[Result "1-0"]
[Annotator "David Hayes"]
[BlackElo "0"]
[FEN "1k1r4/ppq1Qppp/n1p2n2/2Pb4/P7/6P1/5P1P/1RR2BK1 w - - 0 1"]
[SetUp "1"]
[TimeControl "0"]
[WhiteElo "0"]
1. Rxb7+ Kxb7 2. Bxa6+ Kb8 ( { Black can try: } 2... Kxa6 3. Qxc7 { White wins
with a large material advantage. } ) 3. Rb1+ Ka8 4. Qxc7 Rd7 5. Qc8# ( 5. Rb8# ) ( 5. Bb7# ) 1-0