In the Portisch-Radulov game, what does White play after 23...h6 (less obvious than 23...f6 since the h6 pawn is undefended, but it works because the white queen dare not give up defending the e2 square)? Note that 24.Qxh6 not only fails to win, but might actually lead to a losing position after 24...Re2. How does White meet the threat of 25...Rxg2+?

23.Nxd6 might still turn out to be a playable move, but 23...f6? seems to be a weak response by Black - very nicely refuted by White's brilliant 24.Re1. Just the same, for 23.Nxd6 to work White needs a good answer to 23...h6!

Therefore, I prefer the more straightforward 23.Qh6. Unlike 24.Qxh6 in the line above (after the improvement 23...h6), this move threatens mate in one because White's knight hasn't moved from e8. Now 23...Bf8 (better than 23...Qxe8 24.Bxf4) 24.Qxc6 Bxc6 25.Bf4 Rxe8 should give White an edge, albeit a small one (certainly not a winning advantage, though).

What do you think, Peter? Is there a flaw in the solution to this puzzle?

My computer gives a similar analysis.

23...h6 was played in Stempin-Radulov, Rubinstein memorial 1982 and again in Jacoby-Radulov, Hamburg 1984. Radulov won both of these games. So it looks like Radulov worked out the improvement himself after losing the game to Portisch - and got the opportunity to play it twice!