That's a Torre's Attack version. C3 is played to strenght the center, supporting d4 pawn. C4 is also good, it will be transpose to a queen's gambit. Bd3 is good too. In my opinion, none are better than others, its just a way to play. Cya.
c3? Why not c4?
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I am looking at the following game. White played Bd3 at move 6, and Stockfish has c3 instead. I have never considered this before so it boggles me.
Is there a basic fundamental reason why c3 is better here?