Chess Opening Theory/1. e4/1...e5/2. Nc3/2...Nf6/3. f4/3...exf4

=Vienna Game= Black's move is a mistake. White should now play /4. e5/, forcing Ng8 (4...Qe7 solves nothing because of 5. Qe2).

Theory table
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1. e4 e5 2. Nc3 Nf6 3. f4 exf4