A puzzle for the Bank Holiday weekend #chess

This puzzle emanates from the tweet below by my friend GM Stuart Conquest, the organiser for the last several years behind the world's best open, the Gibraltar congress.

This was intriguing, so I wrote to Stuart and asked him which Larsen book he was reading: it was the old edition of his games published by Bell; fortunately, I had it in my collection (I think the number of chess books I have counts as a collection, but the number is withheld in case my wife reads this blog).

 

Puzzle: find the error in the analysis below

Positon before 28…a5

(To make it more enjoyable, consider solving it as I did, and how Stuart did, with a board and pieces).

 

Solution

 

 

In the above positon, black has just played 1…d5-d4, and Larsen plays the natural recapture, 2 cd. However, and I wouldn't have spotted it hadn't Stuart tweeted, a Purdy player would alway examine all biffs and look for jump biffs. Here, there is a jump biff Bg5-d2, and there is a biff Qh7, so 2 Qh7+! Kh7[] (2…Kf8 3 Qh8 mate) 3 Rh3+ and 4 Bd2. The position is roughly level, as it is in the line Larsen gives, which is why Stuart says it is a small error.

Before posting this blog, I checked Megabase 2012, where the game is annotated by Ftacnik: he merely repeats (and cites) Larsen's line.

The line Larsen gives is defensible. It ends (after Qf4):

 

If 34 Rf3 Qd2 35 Ree3 black has to play 35…h5! when after 36 Bg7 Kg7 37 gh Re6! white's open kingside and black's active queen means that white just can't break through: for instance 38 h6+ Kg8 39 h7+ Kg7 40 Rf7+ Kf8 41 h8(Q) Rh8 42 Qh8, when Qd1+,Qg4+,Qd1+ is perpetual.

In conclusion, thanks to Stuart for finding the error. It is a useful reminder to not recapture automatically, something we all do (or, at least I do): and one more example, not the it is needed, of the wisdom of Purdy's maxims.