Blackmar-Diemer Gambit

Named after Armand Blackmar and Emil Josef Diemer: White sacrifices a pawn with 2. e4 and follows with f3 to open lines.

It is reached after 3 moves: 1. d4 d5 2. e4.

Black is to move and has 28 legal moves. Over the next four moves — two for each side — the game can branch into 1,136,220 different games. Those games reach 371,837 different positions: most positions can be reached in more than one way, 3.1 on average.

The Lichess opening list names 48 further lines after this position, such as Lemberger Countergambit (2... dxe4 3. Nc3 e5) and Blackmar Gambit (2... dxe4 3. f3).

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