Four knights - Gunsberg variation
1. e4 e5 2. Nf3 Nc6 3. Nc3 Nf6 4. a3
White pushes the king's pawn to e4. Black plays the king's pawn to e5. White develops the knight to f3.
Black develops the knight to c6. White transfers the knight to c3. Black jumps the knight to f6.
White moves the a-pawn to a3.