4...Bb4 is called the Ragozin, generally considered strongest for White is 4. Qa4+ because this forces Nc6, putting the knight in front of the c-pawn, which is undesirable in d-pawn openings. After this White can play e3 and Bd2.
Something like this could happen. Black is supposed to play 7...dxc4, that is the theory move, but a lot of players are reluctant to do this because they want the f1 bishop to move before they take so they can gain a tempo. In the final position White is a bit better, Black is cramped and e5 is currently unplayable due to the weakness of f7, White has Ng5 and Qb3.
Black shouldn't trade on c3, but if he does Bxc3 is the way to go.
some lines keep repeating...
playing white, i often open with the queen's gambit.
the 1st lines :
1. d4 d5
2. c4 ed
3. c3 f6(?)
Irrespective of whatever black plays as from 3 onwards, his playing e6 opens up for his bishop to go on b4 and pin or attack my knight on c3.
Now the obvious move to prevent this would be to place a pawn on a3, as move no.4.
However I feel much of white's advantage is the momentum, and the tempo as one develops. Whenever I play this, I feel that white has passed the tempo to black, having more pieces on the board and a better advantage to attack and put me in a defensive position. my moves might eventually become a reaction to black's, instead of the opposite.
The order of sequence doesn't make much difference, as black could play bishop as a 3rd or 4th move, and so for myself with the pawn on a3... however the dynamics are the same.
Another option I sometimes choose, being away from the action - is to keep developing my pieces and ignore (usually by placing Nf3), then after placing my black squared bishop on d2, eventually trade. For some reason, I usually prefer taking the bishop back with pawn b2 x c3 rather than the bishop. I feel this opens a lane on the b column for the rook, and the upside down 'V' shaped pawns, with the bishop at the base, creates a solid barrier and defence.
A downside is that the bishop would then not have much use, apart from keeping the pawns toghether as a fortress..
I realise these might be standard book opening sequences, and they are what they are... however the reason I'm writing is to pick your brains on what works for you, on any other doors that I might be missing, what could best give an edge to white as the piecess develop leading to middlegame...
Any insight is appreciated, thanks.