Holy guacamole, what a game! Nice tactical sequence after 30a1-f1.
Going back to my main obsession: in this particular example, I see that if black takes on c3, it only helps white develop. He recaptures with the knight on d2, and frees the bishop. Correcto? Maybe that's another general principle, avoid the trade BxN if white can recapture with his other knight...
#11
In general a bishop is worth more than a knight, but doubled pawns are worth less than non-doubled pawns. So ...Bxc3 bxc3 the pawn structure and the bishop's pair somewhat even out.
Of course if you play 3...Bb4 you must be prepared to part with your bishop, otherwise you could as well play it 3...Be7 right away.
White has several ways to prevent the eventual doubling of his pawns.
1) e3 and Nge2
2) Qc2
3) Bd2
4) Bg5 and Rc1
In those cases parting with the bishop ...Bxc3 must be compensated by another advantage, usually firm grip over square e4.
On the trade ...Bxb4 itself there are 3 considerations in order of decreasing importance
A) The bishop's pair is strong in open positions, so black should try and keep the position closed after he trades.
B) If the pawns are on black squares: d6, e5, c5, then Bb4 is a bad bishop on the colour of its own pawns and it is not that painful to part with it. If the pawns are on white squares: e6, d5, then Bb4 is the good bishop and it is worth preserving it if possible.
C) Retreating the bishop loses a tempo and waiting for white to prompt with a3 gains a tempo compared to taking ...Bxc3 unprompted. A tempo is valuable in an open position and less so in a closed position. As according to A) black aims for a closed position, so consideration C) is less important than considerations A) and B).
One cannot really make up rules:
In this position there are two main lines, taking and Be7:
Playing chess well has always something to do with fantasy and humour.
Yet another witty line, opening the same in my game against GM Sanikidze. He played better though, see above. Black is fine.
#9 and #14 are other counterexamples of the "take if prompted" rule.
#13 both are possible, but black results are better if he retreats ...Be7 and only GM Akopian seems to take ...Bxc3.
Also in the position of #1both are possible and ...Bxc3 is even played more than ...Be7. Carlsen has played both, originally ...Bxc3 and later ...Be7, so I guess he came to the conclusion that in that position the retreat ...Be7 is better.
