Solution to Yesterday's Puzzle
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Solution to Yesterday's Puzzle

Illingworth
GM Illingworth
Oct 9, 2018, 10:03 PM |
5

The post I initially wrote for today ended up being quite long, so I've saved it for tomorrow, and today I'll focus on the solution to yesterday's puzzle. In case you missed that post, here is the position again, with White to play:

9.b4!, as pointed out by several of the commenters to yesterday's post, is the key move, with the prophylactic idea of preventing ...c5. Other moves will allow Black to play ...c5 and ...Nc6, targeting White's center and showing up the a5-pawn as a weakness. 

That explains why 9.Nh4?! c5 10.Nxg6 hxg6 11.c3 Nc6 is promising for Black - the a5-pawn can't be saved, as Black threatens not only a5 but also the ...Qh4 fork. But we should note that, if White had played Nd2-f3 instead of a4-a5, he would have a serious positional advantage - the ramifications of that would entail a whole other post! 
A dream position for White in the Short Caro-Kann

It's also worth noting that, in the puzzle position, even if White didn't have 9.b4!, 9.c4 would be a decent move, even though 9...dxc4 10.Bxc4 Nd5 gives Black a nice outpost for his knight. The reason is quite subtle, lying in the fact the d7-knight is rather dominated by White's pawns, and in turn, blocks subsequent pressure on the d4-pawn in the middlegame.

Once again, this structure would take a whole other post to do justice to, but in the meantime, I'll include the game  @Aradhya2000 referenced in his comment yesterday: 
You can find a professional analysis of this game by Evgeny Postny in Mega Database 2012 or later.

The model game for White after 9.b4 is as follows, which incidentally verifies the point  @vinniethepooh made about the ...f6 break favoring White:
Those of you with Mega Database 2017 or later can look up the game in the database, and enjoy Sumets's detailed and clear annotations. 

One reader was unsure what to do if Black plays ...b6 in reply to 9.b4. It's a fair question, but we can say that there are clear strategic and tactical drawbacks to this exchange of pawns.

Concretely, after 9...b6 10.axb6 Qxb6 11.c3, Black's a6-pawn is quite weak, and if White can get in Nbd2-b3, I would go as far as to say Black is strategically lost (White will pile on the a6-pawn with his pieces). Therefore, 11...a5 is logical, but after 12.Nbd2 (the pawn is still pinned) 12...Qd8 13.bxa5 Rxa5 14.Ba3, it is obvious that the opening of the position substantially favored White, as he has almost finished his development, while it's far from obvious how Black will even get castled. 
Pinning and Winning!
As for  @wingchun1's question yesterday - we saw in this article how having model games to follow makes it much easier to come up with a good plan or transformation of the position once we are out of 'book'. If you are really stuck, try using Aagaard's three positional questions, which I will probably discuss in a later blog post. One could give a similar answer to the question @WilliamShookspear asked, although again, I would prefer to incorporate it into a post more closely related to the initial question. 

I won't give away the subject of tomorrow's post yet, but I'll offer a hint. It relates to the following video:
You'll find out the connection tomorrow!