Ruy Lopez:Open

Black takes the e4 pawn with 5...Nxe4 and opens the game, accepting a lively position with active pieces.

It is reached after 10 moves: 1. e4 e5 2. Nf3 Nc6 3. Bb5 a6 4. Ba4 Nf6 5. O-O Nxe4. It is a line of the Ruy Lopez.

White is to move and has 25 legal moves. Over the next four moves — two for each side — the game can branch into 943,423 different games. Those games reach 328,733 different positions: most positions can be reached in more than one way, 2.9 on average.

The Lichess opening list names 33 further lines after this position, such as Morphy Defense, Tartakower Variation (6. Qe2) and Knorre Variation (6. Nc3).

The same moves can be played in 420 different legal orders that all reach this position. For example 1. Nf3 e5 2. e4 Nc6 3. Bb5 a6 4. Ba4 Nf6 5. O-O Nxe4, which starts as the Zukertort Opening.