Find the computerish idea

[MartinCarpenter]

Something gently mind boggling that turned up when going through the ashes of a rather unmemorable evening league game.

5rk1/pp4p1/3b2p1/3pR3/2pP4/2P2P1q/PPQ2P2/4R1K1

Black to play and..... get searched for electronic equipment

It doesn't win outright by any means but does seem to retain rather more workable chances than anything else. Bonus points if you can somehow explain the 'logic' behind it and why it is seemingly the only move that does it.

In practice I'd been losing for ages and was a bit shocked to have escaped with the rather obvious sac that had just landed so just chopped on e5 and offerred a draw. Odd season. I'm playing quite awfully a lot of the time but having outrageous luck to compensate. Can't remember anything like it.

[Ian Stephens]

Hello Martin, at first glance I would try ...Rf5 blunting the Queens scope and threatening ...Rg5+ or is that too human?

[Christopher Kreuzer]

Er, something like 1...Kf7, trying to bring the rook to h8? I don't think it works, but it is the only 'crazy' move I could find that might work, but 2.Qe2 seems a strong reply, so I'm not sure what the idea is if it is not that.

[Matt Mackenzie]

1....Rf5 was my first thought too - but a bit *too* obvious, perhaps?

[David Gilbert]

What about Rf6 and if White allows follow up with g5, threatening Rh6. Just a thought?

[Brian Valentine]

It looks as though f4 slows down the Rf5 idea, so I'm wondering about ...Kh7 and if Re3 then Rf4 ( ->h4 etc)

[MartinCarpenter]

Yes, Rf5 is far too human. You'd probably even consider it a normal candidate move

Rf6 is actually the move so well done(?!) to David. The main idea of it isn't to attack though. Its to avoid swapping queens......

After Rf6 white seemingly has to go Qe2 - else the attack does get dangerous - and then black can play Bxe5 Qxe5 Qxf3 and retreat to f5 after Qe2. This is, I believe, somewhat non obvious If you take on e5/f3 directly then Qe2 squaps queens.

Why you have to start with Rf6 and not something else, like g5 (which white can't take of course) or Kh7 etc is not very obvious even after briefly looking at its main lines. Probably there isn't really any logic, just a bunch of concrete lines.

[Roger de Coverly]

Rf6 is actually the move so well done(?!) to David. The main idea of it isn't to attack though. Its to avoid swapping queens......

It's going to depend on your engine, computer and settings as Bxe5, followed by Qxf3 is the obvious continuation even to engines. Having "forced" Rf6, there's next to nothing between the evaluations.

[MartinCarpenter]

Ah, Stockfish was very firmly about half a pawn better for Rf6 than anything else ~-0.9 vs -0.4.

So I was presuming it should be something real. Could be an evaluation engine quirk though, yes Fast computer so it might be some deep tactic that justifies it vs some of the other moves.

[Roger de Coverly]

Fast computer so it might be some deep tactic that justifies it vs some of the other moves.

Horizon effect or different weightings then. The hidden idea presumably is the threat of a transfer of the Rook to the h file in support of a mating attack.

Anand, I think it was, cautioned against over-reliance on engine assessments. He reckoned five years later you got a different answer as the evaluations got more sophisticated and the machines faster and deeper.

[MartinCarpenter]

'Static' computer evaluations tend not to mean terribly much. Picking on a move like this means there's a reason. Not always a good one but fun to unpick the (twisted) computer logic whatever

I'm not totally sure about this being strictly right as its based on a bunch of rook endings. Computer aren't great at evaluating those and I'm no doubt quite a bit worse....

Of the moves: Even thinking of 1.. Rf5 clearly shows carbon based thinking as white can just play Rxf5 1 .. g5 probably should be in range of humans too as white can go 2 Re1e3 Bxe5 3 Rxe5 Qxf3 4 Rxg5.

1... Kh7 is more forgivable. The problem there is that white can go 2 Re1e3 and meet 2... Bxe5 with 3 f4 Qg4+ 4 Rg3 Qxf4 5 Qxg6+ Kg8 6 Qe6+ Qf7 7 QxQ+ RxQ 8 PxB etc. 'Obvious'....

So maybe 1.. Rf6 is a waiting move to prepare for 2 Re1e3.... After 2 Re1e3 Bxe5 3 Rxe5 Qxf3 4 Qe2 QxQ 5 RxQ you can go Kf7 and the rook is very well placed for the ending with f5/b6 to pick from. Much better than on f8.

The most likely horizon effect candidate would be that 1.. Rf6 2 Qd2 g5 wins. Takes my comp a few moments to work through that. No wonder really - after 3 Qxg5 you have to go 3.. Bxe5 4 Rxe5 Qxf3 or 4 Pxe5 Rh6. Not clear cut wins.

I spent a while rather puzzled why it felt that 1 .. Rf6 2 Qe2 Bxe5 3 Qxe5 Qxf3 4 Qb8+ Rf8 5 Qg3 QxQ+ 6 PxQ was a non trivial improvement on 1.. Bxe5 etc. That's actually the same position except for whites f2 pawn being on g3. However the clear second rank means that 6 .. Rf6 7 Re5 Rb6 8 Rxd5 Rxb2 9 Ra5 a6 10 Ra4 b5 is now winning due to the b4 breakthrough. So white has to defend a bit more passively instead. Its a seriously hard game sometimes