411 REFERENCE · Wikibooks
Chess Opening Theory/1. e4/1...c6/2. Nc3/2...d5/3. Nf3/3...Nf6/4. e5/4...Ne4
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Caro-Kann Defence: Two Knights Attack B10
4...Ne4 · Caro-Kann Defence: Two Knights Attack
The advanced knight appears threatening, but Black doesn't need to worry about the positions after White captures it with 5. Nxe4, although this move is quite common at amateur level. After the capture and exchange, the white knight on g5 is misplaced, and Black is comfortable. 5. Ne2 and 5. d4 are the main lines.
Theory table
5. Ne2 5. d4 5. Be2 5. Qe2 5. Nxe4 dxe4 6. Ng5 Qd4 5. d3
Caro-Kann