## Sunday, December 11, 2016

### Deep pin

Alright, after a cumbersome begin, we finally have a place to start from. A coat rack to hang our knowledge on.
• Value
• Defenders
• Geometry
• Initiative
• Target placement
• Exploiting immobility
• Opening of the line of attack
• Connection to other tactical themes
As you see, I have added an extra clothes hook to the coat rack: Connection to other tactical themes. In a combination, a pin is often interlocked with a preceding tactical theme and/or a following tactical theme. To keep matters simple, I define a target as a piece, not as a square. Squares as the goal of a pin are treated when I describe the connection to other tactical themes. Since squares are the connection points to other themes.
Let's have a closer look to the pin from our starting point.

 Diagram 1. White to move
Alas, Lucas chess doesn't allow positions without a king. Be not distracted by the fact that it looks like a chess position. Imagine the white king isn't there. When the positions become more complicated, I will otherwise have to add pawns to prevent alternative variations. We talk about winning a target. About concepts. Not about that the position is a draw anyway.

Here you see a duplo attack at full force. 1.Bh2 attacks two targets with one move. One target is attacked directly, the other target indirectly. It wins because black needs two tempi to save both targets in one move. This is a clean pin. Black has no defensive resources whatsoever at his disposal.

Value
What can we say about value in the above in the position above?
• The value of the attacker doesn't matter
• White wins the piece with the lowest value since the other piece can escape
• If the value of the head piece is lower than the tail piece we call it a pin. Otherwise we call it a skewer.
The values in the clean (=without defensive resources) position above I call the pure values. As opposed to calculated values. Actually it doesn't matter that we talk about a pin here. The answers are the same for any duplo attack. Imagine that the white bishop was on a3 in stead of g1. Then 1.Bd6 would be a double attack. With the same result as the pin, black will use the single tempo he has at his disposal for saving his piece with the highest value. If there are no defensive resources, then the two first answers given above say everything there is to say about value. Not only for pins, but for any duplo attack.
Now let's add some defensive resources.

Defenders
Maybe I'm going to treat the following not in the most efficient order, but I have no way to know beforehand what the right order will be, or what will proof to be redundant. So you will have to bear with me. In the later to write summary I will make it up with you.

 Diagram 2. White to move. Imagine as if the kings aren't there.
First scenario: the tail piece protects the head piece.
If white plays 1.Bh2, we can no longer make use of the pure value of the black pieces. If a piece is defended, the value to gain by capturing it, is calculated as target -/- attacker (-/- is the symbol for the minus sign). In the position above, white doesn't gain anything from the capture of the knight, since the calculated value of the gain is 3 -/- 3 = 0. If the black knight is replaced by a rook, the gain would be 5 -/- 3 = 2 points.

In fact it doesn't matter if the head piece is defended by the tail piece or by any other piece. So there is no need to add a separate scenario for the defense by the tail piece. The tail piece is just another defender.

Second scenario: a protected tail piece
A protected tail piece alters the calculated value of the potential gain to the value of the tail piece minus the value of the  attacker. 9 -/- 3 = 6

Summary
When there are defenders involved, you no longer work with the pure values of the targets, but with the calculated values, which means the value of the target minus the value of the attacker.

Extension
The conclusions above aren't limited to pins only, but can be extended to all duplo attacks.

All the above may sound a wee bit trivial. But it clears the head for what is to come. So stay tuned. . .

1. You are making really deep analysis of pin motif!

1) "Connection to other tactical themes" - without that I would refute your theoretical discussion. It seems you avoid killer argument with a blink of an eye ;) :).

I think you will get the idea that when you want to exploit pin (make any benefits) from this (or these if there are more than one), you have to have another motifs and weaknesses. Otherwise the pin brings no benefits (cannot be exploited to gain an advantage).

2) "Squares as the goal of a pin are treated when I describe the connection to other tactical themes. Since squares are the connection points to other themes" - simply excellent observation! I cannot wait any longer for next of your discoveries! :)

3) "The value of the attacker doesn't matter" - I would add: "as long it makes a pin and attacks the piece - no matter if it is Q, R or B". And it is a funny sentence of mine: "...it makes a pin and attacks the piece". It is impossible to make a pin and not attack the piece, do you agree on that? And what about the position when the piece A pins the piece B, but piece A is absolutelly pinned? Have you thought it over yet? Just my curiosity, no need to answer now.

4) "White wins the piece with the lowest value since the other piece CAN escape" - I am not sure, but if I read (understand) it correctly is should be replaced by "CANNOT" (escape). Am I right?

5) "If the value of the head piece is lower than the tail piece we call it a pin. Otherwise we call it a skewer" - the best explanation what is a pin versus a skewer! Simply great! And what about the situation if the head and tail piece are the same value? Is it a pin or it is not? If not - why?

6) Are you going to consider the case related to the distance between the head and tail pieces? Or the positions with the distance between attacker and a head (pinned) piece? I am using this concept when I explain the positions with the defence against check - the covering (blocking). When your piece (which attacks the K) is very far away from the King - you can have a lot more options to cover the line of attack then it would attack from 3-4 squares from the King. This may sound trivial, but in practice it can be used to evaluate how many piece can block the check (and in our case - change the nature of pin).

It may sound quite strange, but I want to be HONEST: I have never read such a blog of enthusiastic, amateur passionate chess discoverer and tester! Your articles (hundreds of them!) provide a gold mine of ideas, concepts and tested examples! I feel really great when I can sink in your articles and read it many, many times. And I return to the old ones and read these together with the comments. This way I can fire my imagination and create great ideas as well. Thanks for that my chess friend! :) You are my hero - no doubts about it! Keep it up and enjoy the process!

1. 4. Black has only one tempo, but he needs two in order to save both pieces. He must chose which piece to save, so he will save the piece that has the highest value.

5. Excellent question! The word pin means that the head piece is nailed. If both head and tail are of the same value, and both are undefended, than you can't say the head piece is nailed, since you win a piece of equal value anyway. But when the head piece is defended, it's calculated value is less than the pure value of the tail piece, so then it is pinned.

6. At clothes hook 7, opening (and closing) the line of attack, that subject will be treated.

Thanks for the cheering. I really appreciate that!

2. @ Tomasz:

3) . . . And what about the position when the piece A pins the piece B, but piece A is absolutely pinned?

Did you have in mind something like this (from Weteschnik), which I gave back on June 28 in a comment here as an example of Equal or Stronger Threat (EST)?

[FEN: 5k2/6p1/p2q3p/b7/2QB4/7P/P5P1/6K1 w - - 0 1]

Bruendtrup - Budrich, Berlin 1954 (Understanding Chess Tactics - Martin Weteschnik)

There are two absolute pins in succession. A (White Bishop) pins B (Black Queen) against C (Black King); D (Black Bishop) pins A (White Bishop) against E (White King). There follows F (White Queen) forking B (Black Queen) and C (Black King). Although C (Black King) can defend B (Black Queen), B is still captured successfully by F (white Queen) because A (White Bishop) can still project power (even while absolutely pinned itself) IF AND ONLY IF IT IS THE OPPOSING KING WHICH MUST RECAPTURE ON THE PINNED SQUARE. Any other piece defending the absolutely pinned piece could recapture (provided it was not itself pinned).

A strange set of cross pins for an OTB game!

3. While waiting eagerly for the next installment, I ruminated on the following ideas.

Going through Chess Tempo’s Tag Guidelines for tactical problems, I found 5 tactical themes which consist in a connection between three pieces on a geometrical line. The five themes are:

Pin
Skewer
X-Ray (Roentgen)
Discovered Attack
Double Check

(I initially considered including Blocking and Interference, but these themes involve creating a three-piece relationship rather than “seeing” an existing or potential three-piece relationship.)

The general schematic is:

{Line-moving Attacker [Queen, Rook, Bishop]} -----> {Piece 1} -----> {Piece 2/Square}

An important initial “cue” is the geometrical nature of these themes. I have found it helpful to “see” the potential relationships (and, by extension, potential tactical themes) by visualizing the “aura” of a line-moving “attacking” piece as extending from the square that piece is on to the edge of the board, along every direction of movement (forward and backward), ignoring any “obstruction(s)” or “targets” (the number and type of any other pieces whether same-side or opposite-side) that are currently on that line. By extending the “aura” through any and all obstructions/targets, the visualization of potential attacks extends beyond the strict limitations imposed by the chess rules. For example, if one limits “attacks” to a direct relationship between an attacking piece and the attacked piece, then these five themes are eliminated from consideration because there are necessarily three pieces involved in them. There IS a direct “attack” (only in the sense that the attacking piece directly “attacks” the SQUARE on which the in-between piece sits) AND also an indirect “attack” (on the subsequent target piece/square).

Another aid to visualization is to initially ignore the point count value of any and all pieces involved in these themes. A given piece has exactly ONE and ONLY ONE “attacking” (capturing) capability on a given square at any given time. For example, a Queen “attacking” a piece/square exerts exactly the same “pressure” on the target piece/square as a Pawn or any other piece. The relative point count values of the involved pieces enable us to differentiate between the themes for identification purposes, but for purposes of visualizing “cues,” these relative values do not matter; the actual and potential relationships between "attacking" pieces and piece/squares DO matter.

One interesting side effect of this visualization of “auras” is an implicit “looking ahead” (similar to, but not the same as, calculating variations). For example, if the “attacking” piece potentially “attacks” through two same-side pieces to a target piece/square, then that is (essentially) looking ahead 3 moves: the two intermediate same-side pieces must be moved before the “attack” becomes actual on the third move. There is a distinct savings in mental effort when utilizing this idea.

2. Here a nice pin which i had a moment ago ;)

http://chesstempo.com/chess-tactics/60864

The pin has to be created AND to be made resitance-proof

The problem has only 5 ply's
The rating is :
1957.6 with Av Seconds:00:31
1867.9 with Av Seconds:01:18
1768.0 with Av Seconds:02:19
Thats a gain of ~~100 Elopoints by each doubleling of the thinkingtime

The most common errors made by the tacticians are
Move Total
1.Qf8+ 2540
1.Qd5+ 1190
1.Rh1 237
2.Rf8 207

So most of these people did not see the refutation of 1.Qf8+

3. The "cue" to the solution is that a White Queen check can force the Black King on to the same geometrical line (h1-h8) as the Black Queen, allowing an absolute pin by the White Rook.

This is an interesting example of "seeing" two potential pins (the relative pin of the Black Rook and the absolute pin of the Black Queen) but failing to realize the importance of using forcing moves AND at the same time preventing counter-attacks. Only the second potential (absolute) pin brings happiness. Patzer "sees" a pin; patzer applies that pin. Alas, any let up in forcing moves allows Black to stay in the game.

It would seem that preventing counter-play (in this specific position) is more important than utilizing as many tactical themes as possible. Only the more distant (absolute) pin is important. The only other consideration is to keep Black on the hook.