anderssen opening

But don't be mistaken.

In my opinion, 1.a3 is very theorical on the contrary!

White will try to obtain theorical position with a3 useful.

Up to black to find where a3 is not so useful.

That's why for instance 1.a3 g6 is often given, because a3 pretty useless here : not completely but less than 1.a3 e5 and 1.a3 d5.

@poucin - I've seen 1. a3 g6 played against me a few times when I've opened with Anderssen (against opponents rated in the 1600-2000 range), to which I usually reply 2. Nf3 (setting up for 3. d4), or else I play 1. d4 immediately.  In either case, I've gotten good results against it.

To reply with 1. ..g6 seems both passive and committal, so the fianchetto is blunted on the long diagonal by a white pawn on d4 or (if white doesn't set up for d4) by a black pawn on e5.  If the game proceeds to a King's Indian Attack with the colors reversed (as seems likely), then 1. a3 is a useful tempo for a queenside pawn storm, which is common to such games (at least in my own experience).

I think it's a mistake, at least strategically, to try and make the a3 push useless - it is what it is, and it should be taken as-is.  Why would you revert to an opening which with white is otherwise regarded as inferior just to avoid letting a3 be useful?  For instance, you could continue on 1. a3 g6 with 2. e4 f5 3. exf5 gxf5 4. Qh5# (extreme example, but you get the point), and 1. a3 proves useless, but black still loses.  I think it is better to alter an otherwise sound plan to compensate for 1. a3 than to opt for a more dubious one just to prove that white wasted a tempo.

U tell d4 block Bg7 but then u mean KID, Gruenfeld, and all these defence are bad? Non sense.

Games against 1600-2000 rated players don't mean anything anyway.

Personnally i lost a game as black with 1.a3 g6 2.h4 against a strong GM, but i had a good position, the opening was not the problem.

moves like 1.e3 1.d3 and 1.c3 and perhaps 1.a3 are so unpopular because they have relatively little independent value, not because they are bad. they are probably no better or worse than the other first moves barring the top 4 or 5.