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My point is that frequently in queens gambit positions, white will play a3 at some point, and also these positions are difficult to win.
That's a ridiculous reason to suggest that it's a good first (or any number of move) move. White will frequently play f4 at some point also, that doesn't mean it's a good first move. Move order tends to matter, and that particular justification is an obvious fallacy even though it's used as justification in chess literature occasionally when what they really mean that it can be played at the times they're suggesting.
I'm going to claim once again that a3 is rarely a good idea unless an opposing piece is threatening to come to b4 or there is a pawn imbalance on that wing.
Why on earth do you think I claimed it was a good move? I simply said that d5 is not a good response, as it makes a3 a useful move. Useful does not mean good necesarily. a3 might have some ideas later in the game, and while not being good might help white slightly in a d5 position, so black has much more difficulty playing for a win. g6! just destroys a3 though.
its not bad but it doesn't really make much sense it seems to give black a free hand on what opening to choose white would need to know hundreds of positions for no reason at all when he can just choose a normal standard opening and play a3 when the time is right