Chess Opening Theory/1. d4/1...Nf6/2. c4/2...e6/3. Nc3/3...Bb4/4. Qb3

= Nimzo-Indian Defence = White protects the knight while concurrently threatening the enemy bishop.

Theory table
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'1. d4 Nf6 2. c4 e6 3. Nc3 Bb4'