Wednesday, June 24, 2015

Calculating Forcing Moves: Defensive Idea 5 - Counterattack to DEFEND (Idea 3, move)

In this post we’ll examine a position where there is a real threat on the board, and we will create an EGT in order to allow our piece to escape from the attack.  Thus we are counterattacking in order to allow the use of one of the basic defensive themes (Idea 3, move away).

In the following position black just played …Bf8.  White to move.

2kr1b2/p2p3p/2p2p1Q/3n1bpB/P7/6B1/5P2/6K1 w - - 0 1

Let's evaluate the position, and then find and prioritize all of black’s threats.

Evaluation:  White is down three points (white queen vs black rook, knight, and four pawns), and neither king has great pawn cover.   Black is likely to win the endgame, and white will be fighting for a draw if he can survive the next few moves.

Threats:  Black’s threat is the simple capture of white’s queen with 1…Bxh6, and this is our priority for calculations.  

Let's look at the five defensive ideas to see what options white has to defend against the checkmate.

Idea 1 – do something to the attacking pieces (the f8 bishop).  White can capture the bishop (1. Qxf8) but the resulting position is clearly lost for white.  He cannot pin the bishop to something of equal/greater value, and he cannot deflect the bishop.

Idea 1 has generated zero candidate moves.

Idea 2 – block the attacking pieces (the f8 bishop from h6).  White cannot block the attack.

Idea 2 has generated zero candidate moves.

Idea 3 – move the piece being attacked (the white queen).  Aside from capturing the bishop on f8, the white queen can move to five other squares (Qg7, Qxh7, Qg6, Qxf6, Qxg5), however, none of them are safe and all resulting positions are lost for white.

Idea 3 has generated zero candidate moves.

Idea 4 – reinforce/defend the mating square (the white queen).  Defending the queen is not possible here.

Idea 4 has generated zero candidate moves.

Idea 5 – counterattack with an Equal or Greater Threat (of losing the queen).  Looking at the EGT chart from earlier we can see that in response to an attack against the queen there are several options.  An equal threat would be to attack the queen (or threaten to win nine points of material), but that is not possible here.  A greater threat would be check, or a checkmate threat.  White has zero checks, but here there is a common checkmate pattern (Boden’s mate) and white can threaten to execute it (1. Be2, threatening 2. Ba6#)

Idea 5 has generated one candidate move.

In this process we considered several moves but rejected nearly all of them after a quick check, and we have found one specific candidate move:



In an actual game with only one candidate move, we should just play it and calculate the next steps on our opponent’s time.  Let’s just take a moment to look at the next few moves, in particular how black should defend against the checkmate threat after white’s 1. Be2:

I’ll try out a simplified approach to looking at black’s defenses.  I’ll list the defensive ideas along with the calculation/evaluation, and hopefully this will be easier to follow than a purely narrative approach!

Idea 1 – black cannot capture white’s Be2 or Bg3, and cannot pin the Be2.
Idea 2 – black has 5 blocks, but zero moves that “prepare to” block on b7:

  • 1…Bd3 (blocking white’s Be2) 2. Bxd3, and black gives up a bishop and does not prevent the checkmate.  Black can reject this block.
  • 1…Nf4 (blocking white’s Bg3, and threatening both 2…Nxe2+ and 2…Bxh6) 2. Bxf4 (renewing the mate threat) gxf4 3. Qxf4 followed by 4. Qxf5.  Black loses a piece and a pawn with this variation, and black should reject this block.
  • 1…Bd6 (blocking white’s Bg3) 2. Bxd6 and again black gives up a bishop and does not prevent the checkmate.  Black can reject this block.
  • 1…d6 (blocking white’s Bg3, and giving the black king a new escape square on d7) and since there is no checkmate threat, now the queen must move:
    • 2. Qh5/h2/h1 and black is winning the endgame, but white can fight for a draw.  
    • 2. Ba6+ Kc7 (forced, 2…Kb8?! allows white to win nine points of material for the queen with 3. Qxf8 Rxf8 4. Bxd6+ Ka8 (only) 5. Bxf8, the endgame is still winning for black but I personally prefer to keep the connected pawns c6/d6) 3. Qh5/h2/h1 and black is winning the endgame, but white can fight for a draw.
    • NOTE: This is black’s KOTH, since all white replies lead to a winning game for black.  In a real game black could just make this move without calculating further, but let’s see if he has anything stronger!
  • 1…Nc7 (blocking white’s Bg3, and defending the a6 square) 2. Qxf6 Be6 Qxg5, and black still has a material advantage but this is less winning for black than 1…d6 lines.  Black should reject this.

Idea 3 – black has one move and two that “prepare to” move:

  • 1…Kb7 (also defends the a6 square)
    • 2. Qh5/h2/h1 and black is winning the endgame, but white can fight for a draw.  
    • NOTE:  Is this any better than our KOTH?  The only difference I can see between this and our KOTH is this position leaves the black king more exposed.  White probably can’t do much but with the white queen still lurking, why risk it?  We don’t have to reject it as bad for black, it’s just not as good as our KOTH.
  • 1…d6 (giving the black king a new escape square on d7, and blocking white’s Bg3).  We looked at this above – this is already our KOTH.
  • 1…Re8 (giving the black king a new escape square on d8) 
    • 2. Qh5 Bg6 3. Qf3 and black is winning the endgame, but white can fight for a draw.  
    • 2. Ba6+ Kd8 (only) 3. Qh5 Bg6 4. Qf3 and black is winning the endgame, but white can fight for a draw.
    • NOTE:  Is this any better than our KOTH?  In fact, I like that this puts the rook on the open file and the pressure on white’s Be2 limits white’s options.  I could consider this to be our new KOTH by a slight edge.

Idea 4 – black has three moves that defend the a6 mate square:

  • 1…Nc7, we looked at this above and rejected.
  • 1…Kb7, we looked above and determined was not bad, but not better than our KOTH.
  • 1…Nb4 2. Qxf6 Be6 3. Qxg5.  Like the other knight move this undefends f6 and allows white to get back two pawns.  Black should reject this.

Idea 5 –  the only EGT to consider would have to start with a check, and black has none.

Let’s take a look at our final chart:



Conclusion.  Creating a checkmate threat was white’s only real candidate move in the original position because it allowed the queen to escape the attack.  The road ahead will be very tough for white, but he does have some drawing chances.

This is the process you should be able to do mentally:  prioritize the threats, use all five defensive ideas to search for specific candidate moves, calculate each one completely, and then pick the best variation based on the final evaluation.

1 comment:

  1. I have just read this post. What I noticed immediately is the bigger clarity of your thoughts. The pointers helped very much to make the text much easier to comprehend (at least to me).

    What you probably missed is a simple addition to the text:

    "there is a common checkmate pattern (Boden’s mate) and white can threaten to execute it (1. Be2, threatening 2. Ba6#)...." [additon] "we assume Black does NOTHING and white mates in the second turn/move. In this position it is the only "two move freeze mate sequence".

    It looks obvious, but I am sure weaker players (like me or much weaker then me) may find it helpful. Anyway your present way of presenting your ideas in the post is much better. Thanks for your improvement! Well done!

    ReplyDelete