Blackmar-Diemer Gambit Accepted

It is reached after 8 moves: 1. d4 d5 2. e4 dxe4 3. Nc3 Nf6 4. f3 exf3.

White is to move and has 36 legal moves. Over the next four moves — two for each side — the game can branch into 1,427,549 different games. Those games reach 485,368 different positions: most positions can be reached in more than one way, 2.9 on average.

The Lichess opening list names 21 further lines after this position, such as Bogoljubow Defense (5. Nxf3 g6) and Teichmann Defense (5. Nxf3 Bg4).

The same moves can be played in 56 different legal orders that all reach this position. For example 1. e4 d5 2. d4 dxe4 3. Nc3 Nf6 4. f3 exf3, which starts as the King's Pawn Game.