Spassky System3

In the Spassky System, 4. e3 Bb7 5. Bd3 c5 has Black hitting d4 at once instead of waiting with ...Be7 or ...d5. With White's bishop on d3 and the long diagonal already covered by Black's bishop on b7, the struggle centers on e4 and on whether White resolves the c5-d4 tension. Castling with 6. O-O is the usual reply; 6. Nc3 and 6. Nbd2 come next. The engine rates it close to equal, and Lichess results are evenly split.