Nimzo-Indian Defense:Rubinstein System

Named after Akiba Rubinstein: 4. e3 develops calmly and keeps all of White’s options.

It is reached after 7 moves: 1. d4 Nf6 2. c4 e6 3. Nc3 Bb4 4. e3. It is a line of the Nimzo-Indian Defense.

Black is to move and has 33 legal moves. Over the next four moves — two for each side — the game can branch into 1,027,906 different games. Those games reach 327,415 different positions: most positions can be reached in more than one way, 3.1 on average.

The Lichess opening list names 50 further lines after this position, such as Normal Variation (4... O-O) and St. Petersburg Variation (4... b6).

The same moves can be played in 30 different legal orders that all reach this position. For example 1. c4 Nf6 2. d4 e6 3. Nc3 Bb4 4. e3, which starts as the English Opening.