## segunda-feira, 26 de fevereiro de 2018

### Xadrez - Mate em 27! (Sam Loyd)

 Samuel Loyd (dedicado a Charles H. Waterbury), American Chess Journal, 06/1879.Código FEN: 8/6pp/1b6/7p/6pr/2N1Pprp/3K1ppn/R4bqk w - - 0 1.

As Brancas jogam e dão xeque-mate em 27 lances!

(White to play and give checkmate in 27 moves!)

PCFilho

#### 3 comentários:

1. This position is illegal; the black pawns could not make enough captures to occupy the squares they occupy in the diagram even if the white king were the only white piece on the board.

1. You're right, Jake. Using retrograde analysis, we find out that this position is illegal, because there are not enough pieces for black to capture, in order to bring the pawns over to their positions.

I think that, if we replace the pawns on g2 and h3 with bishops, the position will become legal, because only 10 pawn captures would be needed. However, there would be two bishops of the same color, i.e., an underpromotion would have to take place.

2. Here's the solution (by the way, I had help with this one!) The solution requires White to control the play with clever tempo plays.

The key 1 Se4! threatens 2 Sxg3 mate. Black's only defense is 1 ... Bc7. Then White plays 2 Rd1, and Black's best move is 2 ... Ba5+. Now White's king makes a trip up the board (the move marked with an asterisk is a deliberate tempo loss): 3 Kc1 (threat 4 Sxg3 mate) Bc7 4 Kb2 Be5+ 5 Ka3 Bb8 6 Kb4 Bc7 7 Kc5 (threat 8 Rd6 (threat 9 Sxg3 mate) Bxd6+ 9 Kxd6 any 10 Sxg3 mate) Be5 8 Rc1* Bb8 9 Ra1 Bc7 10 Rb1 Be5 11 Rd1. Now Black has to move a pawn or he's mated within four moves: 11 ... P move. The last four moves are repeated three more times (again, tempo plays are marked with asterisks):
12 Rc1* Bb8 13 Ra1 Bc7 14 Rb1 Be5 15 Rd1 P move
16 Rc1* Bb8 17 Ra1 Bc7 18 Rb1 Be5 19 Rd1 P move
20 Rc1* Bb8 21 Ra1 Bc7 22 Rb1 Be5 23 Rd1!

Now, since all of the black pawns have moved as far forward as they can go, Black has to move the bishop, and mate follows in four more moves:
23 ... Bb8 24 Rd6 (threat 25 Sxg3 mate) Ba7+ 25 Rb6 (threat 26 Sxg3 mate) Bxb6+ 26 Kxb6 any 27 Sxg3 (or 25 ... Bb8 26 Rxb8 any 27 Sxg3)
The end.

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