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 "Unknown414"]
[Result "0-1"]
[Annotator "David Hayes"]
[BlackElo "0"]
[FEN "r2qkb1r/pQpn1ppp/4bn2/3pp3/2P5/2N3P1/PP1PPPBP/R1B1K1NR b KQkq - 0 1"]
[SetUp "1"]
[TimeControl "0"]
[WhiteElo "0"]
1... Nc5 2. Qb5+ c6 ( { Black can try: } 2... Bd7 3. Qa5 Nb7 4. Qa6 Nc5 5. Qa5 Nb7 6. Qa6 { Draw by repetition of position. } ) 3. Qxc6+ Bd7 4. Qxf6 gxf6 5. Nxd5 Rb8 { Black wins with a large material advantage. } 0-1