[%c_effect f3;square;f3;type;GreatFind;persistent;true] Played after long deliberation, this is the most accurate reaction.
1. d2d4  1... g8f6  2. c2c4  2... e7e6  3. b1c3  3... f8b4  4. e2e3  4... c7c5  5. g1e2  5... d7d5  6. a2a3  6... b4a5 A fashionable move in the Nimzo-Indian Defense. Historically 6...Bxc3 is more popular. 7. d4c5  7... d5c4  8. c1d2  8... b8d7  9. e2g3  9... b7b6 [%c_effect b6;square;b6;type;Mistake;persistent;true] This move is a theoretical novelty. Far from being preparation, the move is probably the result of So confusing his analysis.