Difference between revisions 25881 and 25926 on enwiki

=== Sample Game ===

 +---+---+---+---+---+---+---+---+
 | '''r''' | '''n''' | '''b''' | '''q''' | '''k''' | '''b''' | '''n''' | '''r''' | 8
 +---+---+---+---+---+---+---+---+
(contracted; show full)
 +---+---+---+---+---+---+---+---+
 | '''R''' | '''N''' | '''B''' |   | '''K''' |   |   | '''R''' | 1
 +---+---+---+---+---+---+---+---+
   a   b   c   d   e   f   g   h 


Check again!
White doesn't give black a chance to do anything constructive.
Let's review the three ways to get out of check:
#Capture the piece giving check.  Black could play 7... Qxd5.  But white would simply take queen with 8. Qxd5+.  With such a huge material disadvantage and an exposed king, black could resign without feeling like a quitter.
#Interpose a piece.  Black could play 7... Be6.  But that would be inadvisable, because the bishop would be defended only once (by black's king) and attacked twice (by white's queen and bishop).  In fact, white could end the game at once with 8. Qxe6++ checkmate!
#Move the king.  Alas, the only square which is not under attack by white is g6, even further into the open.  It beats the alternatives, though.

7... Kg6

 +---+---+---+---+---+---+---+---+
 | '''r''' | '''n''' | '''b''' | '''q''' |   | '''b''' | '''n''' | '''r''' | 8
 +---+---+---+---+---+---+---+---+
 | '''p''' | '''p''' | '''p''' |   |   |   | '''p''' | '''p''' | 7
 +---+---+---+---+---+---+---+---+
 |   |   |   |   |   |   | '''k''' |   | 6
 +---+---+---+---+---+---+---+---+
 |   |   |   | '''B''' | '''Q''' |   |   |   | 5
 +---+---+---+---+---+---+---+---+
 |   |   |   |   | '''P''' |   |   |   | 4
 +---+---+---+---+---+---+---+---+
 |   |   |   |   |   |   |   |   | 3
 +---+---+---+---+---+---+---+---+
 | '''P''' | '''P''' | '''P''' | '''P''' |   | '''P''' | '''P''' | '''P''' | 2
 +---+---+---+---+---+---+---+---+
 | '''R''' | '''N''' | '''B''' |   | '''K''' |   |   | '''R''' | 1
 +---+---+---+---+---+---+---+---+
   a   b   c   d   e   f   g   h 

Now white must think of a way to continue the attack.
He would like to play 8. Qf5+, driving the black king to h6 where it can be cornered and checkmated, but black's bishop is guarding the square f5.
If black hadn't interposed with 6... d5, he would now be subject to a forced checkmate.
As it stands white has to be more creative to keep the initiative.

8. h4

 +---+---+---+---+---+---+---+---+
 | '''r''' | '''n''' | '''b''' | '''q''' |   | '''b''' | '''n''' | '''r''' | 8
 +---+---+---+---+---+---+---+---+
 | '''p''' | '''p''' | '''p''' |   |   |   | '''p''' | '''p''' | 7
 +---+---+---+---+---+---+---+---+
 |   |   |   |   |   |   | '''k''' |   | 6
 +---+---+---+---+---+---+---+---+
 |   |   |   | '''B''' | '''Q''' |   |   |   | 5
 +---+---+---+---+---+---+---+---+
 |   |   |   |   | '''P''' |   |   | '''P''' | 4
 +---+---+---+---+---+---+---+---+
 |   |   |   |   |   |   |   |   | 3
 +---+---+---+---+---+---+---+---+
 | '''P''' | '''P''' | '''P''' | '''P''' |   | '''P''' | '''P''' |   | 2
 +---+---+---+---+---+---+---+---+
 | '''R''' | '''N''' | '''B''' |   | '''K''' |   |   | '''R''' | 1
 +---+---+---+---+---+---+---+---+
   a   b   c   d   e   f   g   h 

Again white finds a strong continuation.
White is threatening to force the black king to h6 after all with h5+.
Also the pawn protects the g5 square which is important in some mating combinations.
Finally, there is some chance the rook will be able to join the attack down the h-file.

8... h5

 +---+---+---+---+---+---+---+---+
 | '''r''' | '''n''' | '''b''' | '''q''' |   | '''b''' | '''n''' | '''r''' | 8
 +---+---+---+---+---+---+---+---+
 | '''p''' | '''p''' | '''p''' |   |   |   | '''p''' |   | 7
 +---+---+---+---+---+---+---+---+
 |   |   |   |   |   |   | '''k''' |   | 6
 +---+---+---+---+---+---+---+---+
 |   |   |   | '''B''' | '''Q''' |   |   | '''p''' | 5
 +---+---+---+---+---+---+---+---+
 |   |   |   |   | '''P''' |   |   | '''P''' | 4
 +---+---+---+---+---+---+---+---+
 |   |   |   |   |   |   |   |   | 3
 +---+---+---+---+---+---+---+---+
 | '''P''' | '''P''' | '''P''' | '''P''' |   | '''P''' | '''P''' |   | 2
 +---+---+---+---+---+---+---+---+
 | '''R''' | '''N''' | '''B''' |   | '''K''' |   |   | '''R''' | 1
 +---+---+---+---+---+---+---+---+
   a   b   c   d   e   f   g   h 

Black plays the best defense.
The white pawn is blocked from further advances, and the king has a new escape square on h7.
White's position is still overwhelming, but there is no immediate way to checkmate.

Now let us take a step deeper into chess reasoning.
White knows he is winning and wants a quick kill, but can't see how to get it.
He is annoyed that the black bishop on c8 prevents him from playing 9.Qf5+ and administering the coup de grace.
Therefore he asks himself, what if the were no black bishop on f8?

9. Bxb7

 +---+---+---+---+---+---+---+---+
 | '''r''' | '''n''' | '''b''' | '''q''' |   | '''b''' | '''n''' | '''r''' | 8
 +---+---+---+---+---+---+---+---+
 | '''p''' | '''B''' | '''p''' |   |   |   | '''p''' |   | 7
 +---+---+---+---+---+---+---+---+
 |   |   |   |   |   |   | '''k''' |   | 6
 +---+---+---+---+---+---+---+---+
 |   |   |   |   | '''Q''' |   |   | '''p''' | 5
 +---+---+---+---+---+---+---+---+
 |   |   |   |   | '''P''' |   |   | '''P''' | 4
 +---+---+---+---+---+---+---+---+
 |   |   |   |   |   |   |   |   | 3
 +---+---+---+---+---+---+---+---+
 | '''P''' | '''P''' | '''P''' | '''P''' |   | '''P''' | '''P''' |   | 2
 +---+---+---+---+---+---+---+---+
 | '''R''' | '''N''' | '''B''' |   | '''K''' |   |   | '''R''' | 1
 +---+---+---+---+---+---+---+---+
   a   b   c   d   e   f   g   h 
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