Chess Opening Theory/1. e4/1...e5/2. Nf3/2...Nc6/3. Bb5/3...a6/4. Bxc6

= Ruy Lopez, Exchange Variation = White decides they don't want to risk having their Bishop trapped on the queenside, and exchanges it with black's Knight. Black's only good move is 4...dxc6, as 4...bxc6?! leaves white with a small advantage.

Theory table
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 * 1.e4 e5 2.Nf3 Nc6 3.Bb5 a6 4.Bxc6