# Puzzle of the week #81

Level:
5-Queen
Chess Diagram:

[Event "Puzzle #81"][Date "2009.08.07"][Result "1-0"][SetUp "1"][FEN "1q6/7k/4N3/8/7K/Q7/8/8 w - - 0 1"]

Episode #3 in our journey into of Troitsky's magical World of endgames brings us to the above position. It was published in the chess magazine "Shahmatnoe Obosrenie" in 1910 and still we can find quite a few similar ones in today's junior games; by the time they reach it, both players are mostly tired and usually a mate in one or a simple tactic ends the game. The same happens here. Your tasks:
a) White to move and win
b) What tactical elemente were used to find the solution?

Total available points for this puzzle is 15. The answers will be published next week together with puzzle #82.

Puzzle #80 solution:
This time I have chosen a combination of answers; here they are. Rick's solution for the main line:
In this position, I see that Black's b3-passer will promote before White's c5-passer does, but White will gain a tempo because promoting his pawn checks the Black King. After that, White must keep the initiative or give checks so Black can't start his own plan.
Also see Andy's solution for the secondary line with 1... Be4

[Event "Puzzle #80"][Date "2009.07.31"][Result "1-0"][SetUp "1"][FEN "k3K3/7b/8/1pP5/8/1p5B/8/8 w - - 0 1"]1.c6 b2 {Rick} ({Andy} 1...Be4 {Black loses if he tries to stop White's pawn or trade his Bishop for it} 2.c7 Bb7 3.Bg2!! Ka7 4.Bxb7 Kxb7 5.Kd7 b2 6.c8=Q+ Kb6 7.Qc7+ Ka6 8.Kc6 b1=Q 9.Qb6#) 2.c7 b1=Q 3.c8=Q+ Ka7 4.Qc7+ Ka8 {This point is where 75% of my thinking went. I've considered Kd8, Bd7, and Bc8, but they all fail. Wait a minute - Black is stalemated! One check will do him in. Let's see if my Bishop can contribute} (4...Ka6 5.Bc8#) 5.Bg2+ Be4 6.Qh7!! {What a funny looking double pin! Going along the h1-a8 diagonal is an absolute pin. White takes advantage of this by using a relative pin along the b1-h7 diagonal. If Black moves his bishop along its pinned diagonal, white will play "BxB+ Kb8 Qb7#". Moving the Queen is also no help, for white can still perform the same checkmate. White wins}

Correct solutions:
Rick - 15 points
Andy Q - 13 points
Alex Ge, Jeremy - 10 points

Standings:
Andy Q - 90 points
Rick - 77 points
Joshua - 71 points
Karl - 39 points
Wilson - 38 points
Alex Ge - 37 points
Jeremy - 25 points
James - 23 points
Katerina, Andy Y - 20 points
Marcus - 19 points
Nathaniel - 18 points
Owen - 10 points

Comment:

Ultimate target: the enemy King