Chess Opening Theory/1. e4/1...e5/2. Nc3/2...Nf6/3. f4/3...Nc6

=Trash Variation (Vienna Gambit)= Black's move is a mistake. White should now play /4. fxe5/, practically forcing Nxe5, after which White will play /5. d4/ followed by 6. e5.

Theory table
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1. e4 e5 2. Nc3 Nf6 3. f4 Nc6