generror: <IndigoViolet> Hmmm, maybe I should consult that book when researching the origins of opening variations :)<6...c4> is an interesting move. Stockfish says it's about equal to the main line <6...Nf6>, but its practical results are actually generally better for Black (about +35%-25%=40% compared to +40%-20%=40%). However, a closer look shows that after the main line <7.Bg2 Bb4 8.0-0 Nge7>, things get unclear: After Stockfish's favourite <9.e4>, the results get *much* better for White (about +45%-20%=35%). However, this moved is played only in 40% of all games, instead, people play a variety of moves that all seem to deserve a "?!" and have good results for Black.
Personally, I find it really strange that <9.e4> is played so rarely, it looks pretty obvious to me -- grab central space, strike at the base of the pawn chain, perfect. However, after <6...c4>, all data indicates that an immediate <7.e4?!> (the Central Break/Rey Ardid variation) equalizes for Black, so maybe people are reluctant to play that later, and this variation has such a bad rep anyway that they don't have a closerlook at it. Also strange is that Stockfish and the results completely disagree as to what move to play after <9.e4> -- Stockfish clearly prefers <9...0-0>, but the results are much better for <9...dxe4>.
So there's still a lot of open questions. I didn't go deep into the variations because the Tarrasch is not something I would play, and it also is rarely played by my opponents. The Swedish variation doesn't seem to save the Tarrasch Defense, but it may be worth a try.