9.  Kt-B3, Castles; 10.  R-K1, Kt-B4 (the Knight is to be posted at K3 to bring the White KKt away from his Q4, whence he prevents the advance of Black’s QP by attacking QB6); 11.  Kt-Q4, Kt-K3; 12.  B-K3, KtxKt; 13.  BxKt, P-B4; 14.  B-K3, P-Q4; 15.  PxP e.p., BxP.  This is the critical position in the Rio de Janeiro defence.  Black has succeeded in eliminating the White centre pawn, and sweeps long diagonals with his Bishops, but the advantage cannot be maintained.  White exchanges the Bishop at Q6, and there remains a backward pawn, which Black will hardly be able to hold permanently.  In practice it has been shown that the end-game should be won by White in spite of Bishops of opposite colours, as Black’s pawn at his QB4 is difficult to defend.

16.  Kt-K4, B-Kt2; 17.  KtxB (not BxP because of BxB; 18.  KtxB, BxP followed by Q-Kt4ch), PxKt; 18.  Q R-Q1 and P-QB4.

The game is much more favourable for Black if he first plays 3. ...  P-QR3, and retains the option of driving the White KB away by P-QKt4, after which P-Q4 can be enforced very soon. 3.  B-Kt5, P-QR3; 4.  B-R4, Kt-B3; 5.  Castles, KtxP; 6.  P-Q4, P-QKt4; 7.  B-Kt3, P-Q4; 8.  PxP, B-K3, 9.  P-B3.

Now Black’s pieces are more mobile, and that is the reason why this system of defence is becoming more popular than any other.

On the other hand, it cannot be denied that Black’s pawn formation on the Q side is weak, and that his centre is less secure.  Whilst White has a pawn firmly posted in the centre, Black has a Knight there which will soon be driven away.  White’s Q4, the basis of his centre, is entirely in his hands, whilst Black’s Q4 is exposed to a steady pressure by the White pieces.  Finally Black’s QKt is unfavourably placed, obstructing as it does the QBP and preventing its falling into line with its fellows.

Diagram 26 shows the position after 9.  P-B3.  The latter move prevents the exchange of the B after Black’s Kt-R4, an exchange which would allow Black to round up his pawn formation with P-QB4.  The experts are not yet agreed as to the best continuation for Black in this critical position.  To be considered are the moves B-QB4, B-K2 and Kt-B4.  B-K2 is preferred nowadays to B-QB4, as QB4 should be kept free for the KKt in case the latter is driven from his dominating position, e.g. 10.  R-K1 and 11.  Q Kt-Q2.  For if in that case Black exchanges the Knights, he only furthers White’s development without doing anything towards strengthening his Q4.

If Black covers the Knight with P-B4, White plays PxP e.p. and Kt-Kt5, rids himself of Black’s QB, and thereby weakens Black’s QP still more.

Kt-B4 would therefore seem to be the best choice, as the QB becomes mobile again after White’s B-B2, nor can White