## Tuesday, July 09, 2019

### The ABC of tactics

 Black to move

In order to solve a tactic puzzle, you need to know your basics well. What are the duplo attacks in this position?

There seems to be a discovered attack to the king. But wat is the target for the bishop?

There is a double attack of the knight.

There is a discovered attack against knight d3.

And there is a discovered attack against rook e4

Do you see how the PLF (PoPLoAFun) system is closely related to the duplo attack?

1. The analysis of PoPLoAFun seems to be from Black's perspective. Is it supposed to be "White to move" in the diagram?

2. BLACK to move

Material is equal

Position is NOT about Pawn promotion. Might be about checkmate, but appears to be insufficient preconditions: the White King is fairly mobile and there is not more than a temporary superiority in attackers vs. defenders due to the potential discovered or double check (h2). Therefore, the position is LIKELY about gaining wood.

PoPLoAFun:

WQh3 = LPDO
WNd3 = B.A.D. (1:1 – WR vs BR)
White PoP = e6 (3:1 – WQ, WR, WBb3 vs BKf2
White LoA = 3 converging LoAs from WQh3, WRe4, WBb3)
White PoP = f6 B.A.D. (1:1 – WBb2 vs BKf2
White LoA = b2-f6; possible additional attacker on B.A.D. f6-square after WQxe6 with check)
Black PoP = h2 B.A.D. (2:2 – Possible double check changes this to 1:2 temporarily)
Black PoP = e4 B.A.D. (1:1 – Bba8 vs f3-Pawn)
Black PoP = f4 square (2:3 – WRe4, WNd3 vs BNd5, BBg3, BQc7)
Black LoA = g8-g1 with double check; c7-h2; a8-e4
Any move by BBg3 is with check, so can gain a tempo.

Attack the weaknesses! Aim for the PoPs and open the lines.

f4 = Potential Black fork from BNd5 on two PoPs, discovering “attack” Bba8 vs WRe4 with tempo
BBg3 = Adequately protected (1:2), so BNf4 would not hang BBg3
BNd5 can move to f4, “protecting” e6 making it B.A.D. (2:2) temporarily, opening LoA from Bba8 directly on WRe4, forking WQh3 and WNd3 which is relatively pinned.

CALCULATIONS based on PoPLoAFun:

1. … Nf4 2. Rxf4 (2. Nxf4 Rxd1+ [Decoying the WBb3 off the diagonal toward e6] 3. Bxd1 Bxf4+ 4. Kf2 Bxe4) 2. … Bxf4+ 3. Kf2 Rxd1 4. Bxd1 Bxe4 5. Nxf4 Qxf4 6. fxe4

How much easier it is to determine what is critical in this position and where to direct ones examination of the position by “SEEING” (1) Which side is to move, (2) Material balance (3) What is/are the overall goal(s) for the side to move? (4) What are the PoPLoAFun for both sides? (5) How can the PoPLoAFun information be used to concoct a duplo attack? (6) What motifs and tactical themes/devices are available which utilize the collected information?

FWIW: This written orderly sequence of “steps” does NOT reflect the actual mental sequence that I followed.

The steps are all there, but the ORDER does not reflect how each observation occurred. I usually saccade (“SEE”) something enticing/interesting (such as “attacking” the White Queen) FIRST and then “SEE” what is possible in the local area of the target. The ORDER is unimportant; "SEEING" everything CRITICAL is all-important.

Notice how much simpler (and many times FASTER) it is to utilize a visual approach than it is to use words to describe what's happening in the position!

3. This kind of positions tell me that it is a good idea to start with the themed problem sets that contain a duplo attack of any kind. I.e. double attack, discovered attack, pin, skewer and Roentgen attack. By the way, what is the difference between a skewer and a Roentgen attack?

4. Tempo asks (hopefully, NOT rhetorically):

"What is the difference between a skewer and a Roentgen attack?"

Conceptually and practically, nothing. A skewer provides an additional constraint on the definition (the indirectly "attacked" piece must be of lesser value. It does not matter in terms of winning material.

Chess Tempo provides these definitions:

Skewer: The player attacks a piece of the opponent, which cannot move without exposing a LESS VALUABLE square or piece behind it to attack. The front (attacked) piece usually moves, allowing the piece behind it to be captured.

Roentgen [X-ray]: An X-Ray attack occurs when one piece attacks a square or piece through another piece. Note that this is not the same as a skewer as the relative two opponent pieces of the piece being attacked through is irrelevant.

A distinction without a difference, IMHO. The relative value of the two opponent's pieces is irrelevant in terms of contacts (Averbakh).

5. I think the Chess Tempo definitions are inaccurate and don't reflect how people actually use either the Skewer or X-ray terms in the wider chess world, as far as I can tell.

Pin, skewer, and X-ray all refer to the idea of attacking a piece through another piece. However, skewer and pin refer to what happens if the defender moves their piece off the line of attack. X-ray refers to what happens when the defender moves their piece *along* the line of attack (e.g., 1 Ra8 x Rd8, Qd5 x Rd8, 2 Qd1 x Qd8). This isn't clear in the CT definition.

The skewer definition is inaccurate because the case of equal valued pieces is generally referred to as a skewer (not a pin), at least when I looked around to check. (It also makes sense in terms of the words used - you usually pin a small thing to a big thing, but you tend to put equal size chunks of stuff on a skewer.) But this is excluded by the CT definition. -- mfardal

6. As fas as I can see and observed - the Roentgen [X-ray] is defined this way:

Roentgen [X-ray]: An X-Ray attack occurs when one piece attacks a square or piece through another piece... and it is related only to the line pieces - especially Rooks and Queens (the exception is the bishop, but conceptually it is inside the range of the practical definition).

Let's have a look at back rank mate: White starts: 1.Ra8+ Rb8 2.Rc8+ Rd8 3.Re8+... and black cannot espace with the King, but he is forced to capture the e8-rook with its own d8-rook. It continues this way: 3...Rxe8 4.Rxe8+ Rxe8 5.Rxe8#.

What do you think about that distinction?