Ptero wrote on 01/31/07 at 18:29:18:


That is definitely the right idea.  The early ...d5 does not work well against the Saemisch pawn structure.  White exchanges on d5 and then slowly prepares a pawn roller by means of Bd3, Ne2-g3, f3, 0-0, Ra2-e2 and so forth.  After e3-e4, Black faces a terrible dilemma: exchange on e4 and give White the central pawn phalanx and half-open f-file, or let e4-e5 come in with subsequent f4-f5-f6.  One defensive idea is ...Ba6 with the exchange of White's dangerous d3 bishop, but it turns out that this doesn't really take much sting out of White's plan.  This was all worked out in the 1950s. 

If you unstand this, you can score a lot of easy points in Swiss events with 4. a3 against the Nimzo.  Innumerable Blacks seem not to understand that an early ...d5 is bad for Black.

This line appears as column 81 in Batsford Modern Chess Openings 14th Ed p413.

MCO has few lines here - main line:

4. cxd5 exd5  5. Bf4 Nf6  6. e3 c5 [here another line is given ...Ne4] 7. Bd3 [or a line with Bb5+] Nc6  8. Nge2 cxd4  9. exd4 Bg4 [sideline ...0-0] 10. f3 Be6 [the note says that 11 0-0 0-0 12 a3 Bd6 limits white to a tiny edge.

The main line is clear up to move 6. All of this looks solid enough, but what do I know?