Chess Opening Theory/1. e4/1...e5/2. Nf3/2...Nf6/3. Nxe5/3...d6/4. Nxf7/4...Kxf7/5. d4

= Petrov's Defence: Cochrane Gambit = Black's priority is to organize his defence and to counter White's attack. Therefore, /5...Nxe4/ is bad (moreover, White can win the knight with 6. Qh5+ g6 7. Qd5+).

There are three strategies to build comfortably the defence:
 * /5...c5/ tries to regain space by attacking the center from the queen side.
 * /5...Be7/ is a first step toward an "artificial castling". This prepares Re8 and Kg8.
 * /5...g6/ prepares a fianchetto. Black will leave the e file open and builds another kind of defence with the bishop on g7. But we may wonder if this will resist a White pawn advance on the king side.

Theory table
.

1. e4 e5 2. Nf3 Nf6 3. Nxe5 d6 4. Nxf7 Kxf7 5. d4