411 REFERENCE · Wikibooks
Chess Opening Theory/1. d4/1...Nc6/2. d5/2...Ne5/3. f4/3...Ng6/4. e4/4...e5
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Mikenas Defence
4...e5!
Black undermines White's center. White needs to take en passant with /5. dxe6/, otherwise Black's queen infiltrates on h4 with check.