Petrov's Defense:Modern Attack

It is reached after 5 moves: 1. e4 e5 2. Nf3 Nf6 3. d4. It is a line of the Petrov's Defense.

Black is to move and has 28 legal moves. Over the next four moves — two for each side — the game can branch into 1,032,179 different games. Those games reach 349,362 different positions: most positions can be reached in more than one way, 3 on average.

The Lichess opening list names 9 further lines after this position, such as Center Variation (3... Nxe4 4. Bd3) and Symmetrical Variation (3... d5).

The same moves can be played in 12 different legal orders that all reach this position. For example 1. Nf3 e5 2. e4 Nf6 3. d4, which starts as the Zukertort Opening.