Bishop pair and single bishop (Bx_6)

There are two things here I am asking about. I am curious why Stockfish is saying to take or not take the knights on c6 and f6 and if the bishop pair is a factor with the first bishop.

I played 7. Bxc6. Why is this bad? Simply because of the bishop pair? Other reasons? Compare that with 13. Bxf6. Since one bishop is gone, does Stockfish not evaluate the second bishop as important on the board? In the game, I thought taking the N on f6 (the rook was already on g8 in the actual game) would line up an attack on my king even though pawns were doubled. So, why take the knight? Why not keep it and use it for a queenside attack while keeping the g file closed?

7.Bxc6 is not the strongest for a few reasons... after bxc6 Black has an excellent central pawn complex. Also it is unnecessary to capture the knight unprovoked - if black challenges the bishop with a6 perhaps you then decide to do it (although I might retreat the bishop instead), but other moves can be played eg. 0-0 or Bg5 to continue developing or even Nd5 if you want to get tricky. Anyway, the main issue is the Bb5 is slightly misplacing the bishop IMO. Qc7 is a standard square for the queen in many Sicilians but black would be less inclined to play it this early if Ndb5 was an option for white. Bb5 takes this option away. 6.Bg5 is normal I think, suggesting that you might damage blacks pawn structure with Bxf6.

13.Bxf6 is interesting... I'm not sure black can do too much with the g file, white can go Kh1 at some point, or g3 possibly. In any case, white now has a great knight on f5 which cannot be shifted by g6 from black. Plus the long term weakness of doubled pawns and the fact the Nf6 was influencing the d5 square. Black would love to play d5 safely and open things up (another common Sicilian theme, if black gets d5 safely he should be doing quite well). But it's not straightforward anyway, black has the bishop pair, semi open g file, but the longer term weakness of the doubled pawns and a slightly airy King over on the queenside. 

"white now has a great knight on f5 which cannot be shifted by g6 from black"

So, this is more of the reason than not having the bishop pair?

"black has the bishop pair"

Ok, how would this relate to white? That is the main focus of this thread, to address bishop pair advantages for white (not necessarily compared to black's bishop pair but more so with other pieces white could have or do without). If you think white's bishop pair is not important here, please state that as well and the reasons for it. 

The main thing I am asking for is on the bishops.

Yes I think the strength of the Nf5 plus the doubled pawns is the justification for giving up the Bf6. 

The bishop pair is not important for white here because of the other factors in the position. A quick analysis check on the position at the end of your line in the first post shows the engine giving about +2 for white and suggesting bombing the queenside with Rb1, b4, Na4 and stuff. The black king is weak over there and white has the tools to attack it, the bishops are not needed to do this. Black on the other hand cannot quickly attack the white king despite having the bishop pair and a rook on the g file. 

"Black on the other hand cannot quickly attack the white king despite having the bishop pair and a rook on the g file."

Are there any indicators of this before move 13 is to be made without calculating it all out? Or does white just think "attack knight, double pawns" and "use knight on f5"?

We've got a terminology problem here.

It isn't CALLED "the Bishop pair" if the opponent also has two Bishops. That's like claiming that you've got a Pawn advantage when the opponent has the same number of Pawns as you do.

Also, I'm not sure where you get the idea that 6. Bb5 is a good move. It isn't. White has several better moves, including 6. Bg5, 6. Bc4 and 6. Be2. The drawbacks of 6. Bb5 include (1) committing the Bishop to an exchange that is in Black's favor, (2) exposing the Bishop to the Pawn push a7-a6 which is a move Black wants to play anyway, and (3) obstructing the b5 square, so that Black can now play Qc7 without fear of Ndb5.

To answer your other question, Bxf6 is double-edged, but not bad. It has good and bad aspects for both players. White gets to ruin Black's Pawn formation on that flank and to create targets for his King-side pressure. Black gets to move his Pawn nearer to the center (by gxf6) and gains the two Bishops... which admittedly are not a lot of use in this current position, but might become important later on if the game opens up.

"It isn't CALLED "the Bishop pair" if the opponent also has two Bishops. That's like claiming that you've got a Pawn advantage when the opponent has the same number of Pawns as you do."

Yes, I know that. So, when Bxf6 was an option there was no second bishop since Bxc6 and bxc6 was played. I was wondering if Stockfish then thought "Ok, now the bishop pair can't be an advantage for white, what use is the single bishop now?" Another way of asking this is if the bishop didn't take the knight on c6, would Bxf6 still have been played or would the bishop pair have been a factor? I think you misunderstood the intent of my question. I am not asking if white should preserve the bishop pair on move 13 (I know there is no bishop pair to be preserved.)

"Also, I'm not sure where you get the idea that 6. Bb5 is a good move."

I never said it was. I was asking if the bishop pair was a factor in NOT playing Bxc6.

Regarding your question as to whether White is likely to play Bxf6 even if he still had both Bishops on the board, yes, he is. 6. Bg5 and later Bxf6 is one of the main lines in the Sicilian Classical.

For example:

Here's a game from the 2002 Russian championship:

https://www.365chess.com/game.php?gid=208337

I stated it "looks like". I didn't say it was good.

Why show the Adams vs Anand game? That's a completely different position (the cxd4 Pawn exchange changes everything), and has nothing to do with the question of whether 6. Bb5 is good in the Classical.

Bb5 was played well before cxd4. How can a future move change everything?

How does a player know "trade bishop only if d4 has not been played or black doesn't play cxd4"?

No, in the Sicilian Classical game the Pawns were exchanged on move 3 and the Bb5 came on move 6.

Here's how it works:

In the Open Sicilian (1. e4 c5 2. Nf3 d6 3. d4 cxd4 4. Nxd4) the Bb5 move is not particularly good. It certainly isn't one of the top three choices, and probably not in the top five.

In the Sicilian Moscow variation (1. e4 c5 2. Nf3 d6 3. Bb5+) the Bb5 move is OK. Not great, but OK.

These are two completely different lines, which lead to completely different types of position. A move that is OK in one of the lines is NOT guaranteed to be OK in the other.

In the Moscow, White can play c2-c3 before d2-d4. This totally changes the nature of the central Pawn exchange. The Sicilian Moscow has more in common with the Ruy Lopez than it does with the Open Sicilian.

Personally, I prefer the Open, not the Moscow. 

"In the Open Sicilian (1. e4 c5 2. Nf3 d6 3. d4 cxd4 4. Nxd4) the Bb5 move is not particularly good. It certainly isn't one of the top three choices, and probably not in the top five."

WHY?

"In the Sicilian Moscow variation (1. e4 c5 2. Nf3 d6 3. Bb5+) the Bb5 move is OK. Not great, but OK."

WHY?

"A move that is OK in one of the lines is NOT guaranteed to be OK in the other."

How do we know why in these two cases?

"In the Moscow, White can play c2-c3 before d2-d4. This totally changes the nature of the central Pawn exchange."

Why can't white play c3 in the classical?

You are making a lot of statements, but you aren't explaining why. 

Why is the Bb5 xc6 exchange inferior in the Open?

In the Open Sicilian (1. e4 c5 2. Nf3 d6 3. d4 cxd4 4. Nxd4) White has traded his d-Pawn for Black's c-Pawn. That's an advantage for Black. In return, he has gained more space than Black, and has gained a move since Black's c-Pawn moved twice (c7-c5, cxd4) to trade itself for a White Pawn that had only moved once. That's the imbalance of advantages in the early opening phase of the Open Sicilian: more central Pawn for Black vs space and time for White.

By playing Bb5 then Bxc6, White is (1) giving Black the Bishop pair, (2) shifting Black's b-Pawn to c6 and thus giving him EVEN MORE central Pawn predominance than he usually gets in the Open Sicilian, (3) giving Black an extra move since the White Bishop moves twice (Bb5, Bxc6) to trade itself for a Knight that only moved once. Black's advantage has increased (it's now a Black d-Pawn vs a White b-Pawn instead of a Black d-Pawn vs a White c-Pawn) while White's advantage has eroded (he has lost that extra tempo that he gained on move 3).

Trading off a pair of minor pieces also erodes White's space advantage. A Space advantage is more relevant the MORE pieces there are on the board, and it becomes increasingly irrelevant as pieces get exchanged.

Why is the same exchange relatively better in the Moscow?

The whole situation is different. In the Moscow, White has not traded off his d-Pawn for a flank Pawn. The Black c5-Pawn is still on the board. So a Bb5xc6 trade would not "increase Black's central advantage"... he has none. It would also double Black's c-Pawns (although doubled Pawns are not automatically "bad", they are double-edged).

In the Moscow, White has not yet played Nc3 (as he HAS in the Sicilian Classical line we are comparing it to: 1. e4 c5 2. Nf3 Nc6 3. d4 cxd4 4. Nxd4 Nf6 5. Nc3 d6 6. Bb5), so White can play c3 before playing d4, and can recapture on d4 with a Pawn instead of with the f3-Knight. This means that Black does NOT get the central Pawn advantage (d-Pawn vs c-Pawn).

Why can't White play c3 in the Classical? Because he has already played Nc3 and that square is not available.

"By playing Bb5 then Bxc6, White is (1) giving Black the Bishop pair"

Ok, so bishop pair is a factor then.

"So a Bb5xc6 trade would not "increase Black's central advantage"... he has none."

So, bishop pair is not a factor in this case?

"Why can't White play c3 in the Classical? Because he has already played Nc3 and that square is not available."

So, c3 couldn't be used to protect the d4 knight if the knight on c3 reroutes to another square later on?

1) Not immediately, but a potential factor if the position should open up.

2) I said "central advantage". That is a matter of Pawn structure, and has no connection with the Bishop pair. White traded off his d-Pawn for Black's c-Pawn. That gives Black TWO remaining central Pawns (both e-Pawn and d-Pawn) while White has only ONE remaining central Pawn (the e-Pawn) plus a flank Pawn (the c-Pawn). That constitutes Black's central advantage.

If you mean: Why is the Bishop pair a lesser factor in the Moscow than in the Open?... it's because the advantage of the Bishop pair is increasingly important the more open the position is; and obviously it's more open in the Open variation... hence the name.

3) Why? Why protect White's d4-Knight with the c3-Pawn? Even if you can afford to move the c3-Knight (losing time and also losing touch with the central squares), what is gained by playing c3? It's too late to reply to c5xd4 with c3xd4... that Pawn trade has already gone by. So what would be the point? Why is White even playing on that side of the board? In the Open Sicilian, White's prospects are in the center and on the King-side.

"what is gained by playing c3? It's too late to reply to c5xd4 with c3xd4... that Pawn trade has already gone by. So what would be the point?"

You stated earlier:

"(2) shifting Black's b-Pawn to c6 and thus giving him EVEN MORE central Pawn predominance than he usually gets in the Open Sicilian"

"This means that Black does NOT get the central Pawn advantage (d-Pawn vs c-Pawn)."

If the c3 pawn goes to d4, then doesn't this help white's "dominance" or ability to fight off a prior black dominance?

The question is ONLY about the bishops. You only need to type "C) you forfeit bishop pair."

Or say "Yes, the bishop pair is a factor".