dzechiel: White to move. Black is up three pawns! "Medium/Easy."Poor Tukmakov! Up three pawns against the likes of Garry Kasparov, and his b-pawn one move away from promotion! What fate is to befall him?
I have been looking at this position for seven or eight minutes now, and I know that I must have considered the key move, because I have considered EVERY legal move for white (and some illegal ones, like 43 Kg1).
Well, now over ten minutes, and I'm not any closer. I'm going to try and look at each possible white move:
- 43 Kh2
If this is the winning key move, then it is perhaps time I took up a new hobby. It allows 43...Ng4+.
- 43 g3 or g4
These moves seem to serve no purpose, but not as bad as 43 Kh2.
- 43 Ra1, Rb1, Rc1, Rf2, Rf3, Rf4, Rf5 or Rd1, Re1, Rg1
The first seven are bad, bad, bad, they allow black to make checking moves that win material. The other three are possible, but they take the rook off of the f-file, which doesn't seem right.
- 43 Bc7
This was one of my candidate moves, but after 43...Rxc7 44 Qd8+ Kg7 I don't see how to make progress towards a win.
- 43 Bb6
Another candidate move. This at least attacks the queen, so it has some oomph. But once again, after 43...Rxb6 44 Qd8+ Kg7 I don't see a winning line for white.
- 43 Bxa5
More of the same, but less forcing.
- 43 Be7
Still another candidate, as it does attack the queen and threaten mate. But after 43...Qxe7 44 Qxe5 b1=Q it looks bad for white.
- 43 Qf8+, Qf7+, Qg7+, Qxg6+, Qh8+, Qf5, Qe7, Qf3
Ways to lose the queen without compensation.
- 43 Qg5, Qh4, Qf4, Qf2
Moves that allow 43...b1=Q without noticeably improving white's position.
This brings us to the first candidate move I considered...
43 Qxe6+
Black has two ways to parry the check:
- 43...Rf7
- 43...Nf7
The first seems good enough for black:
43...Rf7 44 Qe8+ Rf8 or even 44...Kg7.
I don't see a win for white.
It is possible that white is playing for a draw. I did notice in the 43 Bc7 line that there were chances for a perpetual check, eg:
43 Bc7 Rxc7 44 Qd8+ Kg7 45 Qf6+ Kh6 46 Qh4+ Kg7 47 Qf6+. This might very well be the solution.
This is the toughest "Medium/Easy" I can recall. I hope my brain isn't turning to mush in my old age.
Time to check.
b6, also with the idea of perpetual check. Does it work too?
x
e7 preventing that. The subtlety appears to be that 
(45. ... b1Q)
