Interference seems much less common than other types of tactics. In the Polgar brick I noticed that when I find interference it usually is when one piece moves onto an intersection line of 2 defenders, simultaneously blocking both lines and making recapture a problem either way (624/5334 for example). I don't know if anyone calls this double line or multiple line interference, but that seems to be a logical term for it.

This tactic has been difficult for me to spot in games, as I expect it is for many beginning and intermediate players. Repeatedly working through examples may be adequate preparation to spot it more regularly in-game, but I wanted to form a better understanding of it. I played around with it, composing some easy examples, breaking it down into simpler parts. This led me to think single line interference was a better starting place than double line interference. It still is messy! I made a less obvious, more complicated example (above). I hope this example shows that just blocking 1 line alone is enough to throw one out of typical move considerations into unnatural but strong sacrifice moves.

Answer: 1.Qd5! Threatening the smothered mate with 2. Nf7#

(1.Nf7+ is more of a mess as in Bxf7 2.gxf7 Nd7 3.Ng6+ Kh7 4.Qxe4 Kh6 5.Bc1+ Bf4 6.Bxf4+ Kh7 7.Nf8+ Kh8 8.Qh7#)

1...Bxd5 A peculiar result of 1.Qd5! is that Black's Rook and c6 pawn can't occupy the d5 square without creating a f7 vulnerability.

2.Rxd5 Threatening again the smothered mate with 3. Nf7#

2...Nd6 Defending f7 at all costs

(2...Rf8 leads to a quicker mate with the clearance move 3.Nf7+ Rxf7 4.Rh5#)

3.Bxd6 this is the fastest way to get rid of the defender and also keep the Rh5# idea going, which is pretty much now unstoppable

3...Rf8 averting mate for just another move

4.Nf7+ Rxf7 5.Rh5#

[Site "?"]
[Date "????.??.??"]
[Round "?"]
[White "New game"]
[Black "Fritz 8"]
[Result "1-0"]
[SetUp "1"]
[FEN "1n1r3k/1nb1N1p1/1pp3P1/6N1/3Qp2P/Bb6/5P2/3R3K w - - 0 1"]

1. Qd5 (1. Nf7+ Bxf7 2. gxf7 Nd7 3. Ng6+ Kh7 4. Qxe4 Kh6 5. Bc1+ Bf4 6. Bxf4+
Kh7 7. Nf8+ Kh8 8. Qh7#) 1... Bxd5 2. Rxd5 Nd6 (2... Rf8 3. Nf7+ Rxf7 4. Rh5#)
3. Bxd6 Rf8 4. Nf7+ Rxf7 5. Rh5# 1-0

Working on this helped me clarify a detail that I never saw fully discussed in any chess book: outnumbering the long-range pieces on a line and perpendicular. Thinking this way, Black could have stopped the Qd5 interference idea by having one more diagonal protector either along the a2-g8 diagonal or a8-h1 diagonal.

I suppose this kind of outnumbering rarely comes up, as it's extremely unlikely to have more than a Queen and Bishop on a diagonal. Another limiting thing for the defender is the difficulty of using pawns; obviously that only works if the square it's protecting is exactly 1 "forward" diagonal square away. Suffice it to say the attacker has a huge advantage, as he can throw pieces onto the interference square from any direction.

-=-=-=-=-

I am still reading the McDonald book incrementally, and I think it's helping. The continuity of moves and plans he describes continues to impress me. In "Game Two" though, his analysis of 28... f6 seemed a little weak, and Fritz confirmed it (thanks PMD for the file). It just shows that Masters are human, as I think he fell out of a vigilant doubting approach and simply argued for Black's move choice.

Back to solving problems. TCT Circle 4's days are numbered...

TCT Results	Circle 1	Circle 2	Circle 3	Circle 4
Step 1	97%	99%	99%	100%r
Step 2	93%	96%	95%	97%
Step 3	93%	97%	97%	96%
Step 4	80%	86%	90%	92%
Step 5	74%	77%	83%	87%*

Posted at 1:44 PM. Click to see this post's 3 comment(s).