411 REFERENCE · Wikibooks
Chess Opening Theory/1. f4/1...e5/2. fxe5/2...Nc6/3. d4/3...Qh4/4. g3
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Bird's Opening rd bd kd bd nd rd pd pd pd pd pd pd pd nd pl pl qd pl pl pl pl pl pl rl nl bl ql kl bl nl rl
4.g3
This move is forced, as Kd2?? Qxd4+ is obviously horrible for white. Now, he will be left with a doubled e-pawn and a bad pawn structure.
Theory table
+4...
Qxd4 +/-