The subject of today's discussion was inspired by your comments, my dear readers. So let me thank you again for your comments and suggestions. Last week one of the readers suggested an article about long diagonals (a1-h8 and a8-h1). Actually we have touched on this interesting subject in one of the previous articles ( Typical Patterns Everyone Should Know. Part Two.) But there is another diagonal which is much more dangerous in openings and yet not very well covered in chess literature. I am talking about the a5-e1 diagonal. While in a middlegame or an endgame this diagonal is not particularly important, in openings this diagonal is very special. Due to the fact that in most closed openings White fights for the center by pushing his pawns to d4 and c4, he has only two minor pieces (Bc1 and Nb1) to guard this diagonal. And if these two guards forget about their duty... well, the result was shown in the very first example of the last week's column (Pin, unpin). Here is another example where one of the strongest GMs of his time fell victim of this diagonal.
The next recent game (played less than 2 weeks ago!), shows a modern GM falling for a similar trick.
Even when White's minor pieces are ready to defend against the threats along this 'magical' diagonal, a pin can still hurt. The next game of a very young Anatoly Karpov is a good example.
Of course White should be careful not only in the closed openings. Even when White plays 1.e4 and the c2 pawn never moves to c4, he still has to watch out for tactics along this diagonal.
But don't think that if you play Black you shouldn't be careful. The diagonal a4-e8 has claimed many victims too, as the next opening trap demonstrates.
I hope I managed to convince you that the diagonals a5-e1 and a4-e8 should be treated with respect. Be especially careful in such openings as the Nimzo Indian and the Queen's Indian Defense as the Black Bishop lands on the b4 square in most of the lines there. Also we analyzed the typical ways to punish your opponent if he doesn't pay attention to these diagonals. Happy hunting!