Go ahead.
Is 1. d4 d5 2. c4 Bf5 playable?
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I dont think the bishop is stuck behind in the slav. maybe u meant the semi slav?
b7 is weakened by the absence of the Bishop, who is being posted somewhere rather early. It may not have any use there and need reposting later, wasting a move.
Yeah, why not Qb3, white seems immediately better. What's black idea with Bf5?
Funnily enough, I could say the opposite... it abandons some light squares and consequently something really bad does happen (Qb3) 
Surprising to me, my computer says it's not terrible. I guess he who takes the b pawn sleeps in the streets, but I suspect if I let my computer play out some lines white would be better than it guesses.
I guess the whole idea of the Baltic Defence, which I learnt as Grau variant, is that white might not see the need to play Qb4+.
pfren wrote:
3.Qb3 e5 is not so easy for white.
Pawnhunting with all your pieces undeveloped can be very harmful for your health.
The real problem is the unpleasant ending after 3.cd5 Bxb1 4.Qa4+.
Oh- and screw your computer: it will grab a pawn or two, and claim a huge advantage, until it realizes that things are actually not rosy at all.
Actually it was the opposite, my computer eventually took the pawn, but said it was nearly equal. I disagreed and thought white was better
I didn't know about the 3...e5 move though.
The light squared bishop being stuck behind the panws in the Slav and QGA always annoys me. Could I play this and move my pawns later into the Semi-Slav structure?