Recently I have posted a question about declining the Marshall Gambit in the QGD, and asked if Black can transpose into another solid opening, as one way of defense.
After analyzing the first position in the below diagram, I have realized that it can crop in a up specific Caro-Kann move order. What raises my hopes even higher is that White does not play
5.Bc4 there, which means that
5.c4 is weak and has its drawbacks.
Compare the following diagram:
[Title "QGD, Marshall gambit"] [fen "r1bqkbnr/pp1n1ppp/2p1p3/8/2PPN3/8/PP3PPP/R1BQKBNR w KQkq - 0 6"]
and this one:
[Title "Smyslov variation ( B17 ) after 5.c4"] [StartFlipped "0"] [fen "r1bqkbnr/pp1npppp/2p5/8/2PPN3/8/PP3PPP/R1BQKBNR b KQkq - 0 5"]
Although in the second diagram Black has better moves than
5...c6, I believe that favorable transposition can still be achieved.
To determine if this is true, I need to know how Black refutes
Under refutation I consider Black achieving at least a fully equal position.
Hence these questions:
Can Black equalize or achieve advantage in the position from the second diagram?
If answer to the first question is positive, can you demonstrate it with concrete lines?