Ruy Lopez:Berlin Defense, Rio Gambit Accepted

It is reached after 8 moves: 1. e4 e5 2. Nf3 Nc6 3. Bb5 Nf6 4. O-O Nxe4. It is a line of the Ruy Lopez.

White is to move and has 29 legal moves. Over the next four moves — two for each side — the game can branch into 1,114,019 different games. Those games reach 378,393 different positions: most positions can be reached in more than one way, 2.9 on average.

The Lichess opening list names 15 further lines after this position, such as Rio de Janeiro Variation (5. d4 Be7) and l'Hermet Variation (5. d4 Nd6).

The same moves can be played in 36 different legal orders that all reach this position. For example 1. Nf3 e5 2. e4 Nc6 3. Bb5 Nf6 4. O-O Nxe4, which starts as the Zukertort Opening.