he <Once>, too early in the morning?

as mentioned many times above 31.Rxc4 is not possible due to 31...Be1+ winning the queen.

26...Bc4 is a completely different thing than 30...Bc4

30 ... Bc4

31 R7xb4 Be1+ (R1xb4 is worse!)
32 Kxe1 Qxb3!
33 R1c3 Qb5 and black is winning

31 Qe3 Qxc7
32 axb4 axb4
32 Nb6 Ra6

Bxa3 doesn't work as a preparatory move, as the white queen just takes on a3. Then I saw Bc3. Not only does this move put the question to white's queen in a fairly rude way, it seals off white's advanced rook from its fellow, leaving it vulnerable to capture. White could trade that rook for a bishop and pawn, except that the Be1+ maneuver is now ready. So, 30...Bc3 looks like a successful double attack.

As I look at it further, though, after 30...Bc3 31 Qe3, 31...Qxc7 32 axb4, and white doesn't seem so bad. That certainly doesn't look like a great position for black. But if instead 31...Bf8, then 32 Nb6 Nxb6 33 Bxb6 Ra6 34 Rc6, and I think the white rook escapes.

So, I can't find anything better than 30...Bc3 31 Qe3 Qxc7 32 axb4, perhaps followed by 32...Qc6 33 b3 axb4 34 bxc3 Qxa4 35 cxd4 Qa2+, where I would much rather be black, with that nice passed pawn on b4, though white has some counterplay.

This felt puzzle-y enough that I suspect that my first black move is right. After that, I'm not as confident that I found the best line, but I think that mine turns a seemingly difficult position into an advantageous one. If I could to that consistently in real games, I'd probably play more games and do fewer puzzles.

30...Bc4 31 R1xc4 (to protect the Rc7) Be1+ 32 Kxe1 Qxb3 33 Bd1 Qb8 34 Nc5 Nxc5 35 R4xc5. White has BB for Q and a R on the 7th, and is also threatening the desperado attach f5!?, but this should not be enough. Time to check:
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I found the first move, but little else. I missed the best White defence (31 Qe3! limiting immediate losses to the exchange) and also after 31 R1xc4 Be1+ 32 Kxe1 Qxb3 33 Bd1 the best continuation of the Black attack, which is Qxg3+!

Crafty End Game Trainer check of the position at move 30:

click for larger view

White threatens 31.axb4 and eventually Bxd5 exd5 Qxd5 and e6.

The black queen x-rays her defenseless white colleague and Black's LSB can cut the connection between both white rooks if it moves to c4. Therefore, 30... Bc4, with the menace 31... Be1+:

A) 31.Qc2 Qxc7

A.1) 32.axb4 Qb7 - + [R vs B] (32... axb4 33.b3 Qa5 34.Ra1 Ba6 35.Nb6 Qb5 36.Nxa8 Rxa8 - /+ [N+P vs B]).

A.2) 32.b3 Bxa3 33.Ra1 Bb4 34.bxc4 Rac8 - + [R+P vs B].

B) 31.Qd1 Qxc7 looks similar to A.

Konstantin is a GM n 2613 means he is quite a strong one and i would say TOO strong 2 miss such a mate. 37.f6 has ne4+ followed by Qf8 forcing the exchange of queens or another exchange of pieces.

And this tactic often pops up with a pair of rooks (or a rook and a queen), and especially when they are separated by some distance -- as in today's puzzle.

It comes in a couple flavors:

1. Attack both of the mutually defended pieces, and then stick a guarded but lesser-valued piece between them.

2. Attack one of the defended pieces, and then stick a guarded but lesser-valued piece between which carries its own threat (such as this case, where the interfering bishop attacks the queen).

Black to play (30...?) "Medium/Easy"