Nimzo-Indian, 4.e3, Botvinnik System 1. d4 Nf6 2. c4 e6 3. Nc3 Bb4 4. e3 0-0 5. Bd3 d5 6. a3 Bxc3+
In each game under Location you see masterchessopen.com but it's not a valid website, so please don't use it. Claus Gamborg, Jan. 2023