Meduna line in the Colle (proper)

Please let me set the context.  IM Andrew Greet of the illustrious second city of the Empire namely Glasgow has been doing rather well in an international invite tournament, Dundee, Scotland. Yesterday he played GM Keti Grant and employed a super interesting line named after Czech Grandmaster Eduard Meduna as far as I can tell.  Practically the Colle has its most testing time against blacks Kingside finachetto and yet as early as move three white attempts to limit the black options. check it out.

1.d4 Nf6 2.Nf3 g6 3.Nbd2

What is the idea behind this cunning move Nbd2? It appears to me that it commits black to either allowing e4 or preventing it with ..d5.  If black plays something other than ...d5, say ...d6 then white plays e4 next move and gets a position from the pirc defence which has been played by Karpov himself.  In the game Mrs Grant played ...d5 preventing an immediate e4.

After this move white plays a very interesting move which as far as I can tell has been played by some very strong GM's including Harikrishna Pentalis and Maggie Carlsen.  One chessbase article I read named it the Meduna line after Czech Grandmaster Eduard Meduna   The strange looking 5.b4.  

I must admit that I know not what to make of the move 5.b4.  What is its purpose? Its intent? In one respect its easy to discern that it provides a diagonal for the dark squared bishop which will be better placed on b2 or a3 after white locked the chain with e3 making it more active than its counterpart on g7.  Could there be more to this than I am able to discern?  Incredibly interestingly in the game and at least one other game I managed to locate white sacrifices the Queens Rook for the dark squared bishop.  If anyone can shed some insight into this interesting move 5.b4 it would be most appreciated.  I include the full game below with some little annotations.

The Nbd2 move order is aimed to provoke ...d5 and is aimed against Black's counterplay with c5. With a knight on d2 it may be possible in some situations for Black to capture on c5 and keep the pawn with ideas like Nb3 or b4 afterwards.

After 4...c5 5.dc Qa5 6.a3 Qxc5 7.b4 Q somewhere 8.c4 White gets an open catalan with colors reversed which is interesting.

Otherwise the closed catalan plan of ...c5, ...Nbd7, ...Qc7 and ...e5 gives Black a good game even a tempo down.

5.b4 looks to continue to play against ...c5 and prevent the reversed closed catalan.

3...c5 is another idea with the point that after 4.dc Qa5 5.a3 Qxc5 6.b4 Qc7 7.Bb2 Bg7 8.e3 O-O 9.c4 d6 with a reversed Reti.

A problem move order might be 1.d4 d5 2.Nf3 Nf6 3.e3 c5 when Black keeps his options open and White needs to declare his intentions.

4.Nbd2 may be well met with 4...Nbd7 and the typical closed catalan plan although here maybe White can play 5.b3 and argue that Black's knight is better on c6 in such positions and Black will need to play a slower plan of ...b6 and ...Bb7.

4.b3 cd ed leads to typical positions that are ok for Black. He can play plans with ...e6 or ...g6 here.

Maybe 4.dc is worth a punt.

Nbd2 forces the issue of whether black will play d5 or something else.  Even after Nbd2 black can play c5 at any time.  

The entire idea of Nbd2 is to limit blacks options, to allow or not allow an immediate e4.  Very interesting idea.  If black allows it by playing somehting other than . . d5 we get a variation of the pirc defence.  

Yeah but 4...c5 I'm not sure about. In the normal catalan White is able to play against the c-pawn for a long time. Here White can play it immediately. There's also the question of where to put Black's queen after a3 and b4.

If you put it on the c-line then Rc1 will force it to move again.

If you put it on d6 then White has this later plan of Qb3 and Rd1 putting pressure on the queen and forcing it to move again.

And if you put it on b6 then this idea of c4 and Rc1 creates a threat of Bxf6 hitting the d-pawn that the queen can't defend anymore.

Maybe this is ok but it doesn't look all that easy to me.

Sure but the point is after Nbd2 we are forcing black to choose, either to play d5 or not.  If he does then we get the variations that you cite and your ideas are excellent and if he doesn't and allows an immediate e4 we get something entirely different.

This early b4 is reminiscent of similar early g4 ideas in various King Pawn openings.  For instance, the Philidor via the 'Black Lion' move order has a similar thrust on the opposite wing.

The idea isn't just to hack away like a complete caveman, but to gain space, restrict play, create threats ... and then to hack away like a caveman when the time is right.  White has a solid enough centre that Black cannot immediately punish this with the old maxim 'a flank attack is met by a central counter-attack'.  The Keres Attack in the Sicilian is another example, which is practically so difficult to play that many players use a Najdorf move-order to avoid it if they wish to play the Scheveningen.

Without looking at it deeply, my intuitive response is for Black to either seek to neutralize the advance (c6 and then a5, similar to a line in the Solkosky, 1.b4 c6 2.Bb2 a5) or to try central counterplay along the lines of an eventual Ne4, Nbd7, Bf5 in some order, preparing piece play or an e5 break if possible. 

Vewy vewy intwesting Meester Bond!  Although I must point out that the kingside versions seem not a little more potent because they come with the immediate threat to dislodge kings knight. Whether the threat is real or simply perceived I cannot say but it seems that it forces black to take measures to prevent the knight from being hassled with ..h6 or to strike back immediately in the center with ..e5.  What does b4 in the Meduna Colle actually threaten? I know not.  

found it...

The move b4 simply stops an eventual ...c5. Compare with the analogous line (colors reversed) 1.d4 Nf6 2.Nf3 e6 3.g3 b5!? 4.Bg2 d5, which is quite OK for Black.

White should not expect an advantage by this, but surely enough it's a game for both sides. Latest case recorded went well for white (in a top notch rapid game).

Cheers IM pfren, very interesting ideas.  The entire Kingside fianchetto  for white has been somewhat problematic and Colle himself and other practitioners like Koltanowski  I think eventually switched to whites own Kingside fianchetto when faced with it. The double bishop sacrifice was very pleasant to behold!