ECO C42 · Petrov's Defense
Petrov's Defense: Classical Attack, Mason-Showalter Variation
The position after 1.e4 e5 2.Nf3 Nf6 3.Nxe5 d6 4.Nf3 Nxe4 5.d4 d5 6.Bd3 Nc6.
1. e4 e5 2. Nf3 Nf6 3. Nxe5 d6 4. Nf3 Nxe4 5. d4 d5 6. Bd3 Nc6
Petrov's Defense: Classical Attack, Mason-Showalter Variation is filed under ECO C42, a variation of Petrov's Defense: Classical Attack. It is the position after 1.e4 e5 2.Nf3 Nf6 3.Nxe5 d6 4.Nf3 Nxe4 5.d4 d5 6.Bd3 Nc6 — 12 half-moves in, with White to move. Named theory ends here; beyond this the position is yours to work out.