Nimzo-Indian - three knights variation
1. d4 Nf6 2. c4 e6 3. Nc3 Bb4 4. Nf3
White pushes the queen's pawn to d4. Black develops the knight to f6. White pushes the c-pawn to c4.
Black moves the king's pawn to e6. White develops the knight to c3. Black develops the dark-squared bishop to b4.
White jumps the knight to f3.