Chess Opening Theory/1. e4/1...Nc6/2. d4/2...d5/3. Nc3/3...a6/4. exd5

= Nimzowitsch Defence = White has accepted the countergambit and black should now move his attacked knight to b4.

Theory table
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'1. e4 Nc6 2. d4 d5 3. Nc3 a6 4. exd5'