Chess Opening Theory/1. e4/1...e5/2. Nf3/2...Nf6/3. Nxe5/3...Nxe4/4. Qe2/4...Qe7

=Petrov's Defence, Damiano Variation=

4...Qe7
For now, black maintains symmetry (note that four full moves of symmetry is very unusual for an opening). White will be ahead a pawn if he simply accepts the knight, so 5. Qxe4 is almost universally played.

This position is most common among beginners, but the resulting pawn sacrifice is not without compensation and offers decent practical chances, especially in faster time controls.

Theory table
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1. e4 e5 2. Nf3 Nf6 3. Nxe5 Nxe4 4. Qe2 Qe7