(7) Good key, characteristics 11 and 12

Characteristic 11 : The key is give-and-take. Usually we give flights and take equal number of flights, but let us see here a replacement of the sacrificed piece.

	(Problem 8) Stavros Iatridis, Chess magazine “O Skakistis”, issue No.6, May 1968 White plays and mates in 4 moves #4 (6+3)
[8/8/6pR/5kS1/5p2/5P2/6SK/B7]

What it is important : to achieve mate in the number of moves stated in the stipulation. (It is completely unimportant if we can achieve mate in more moves). The golden winner of chess Olympics Stavros Iatridis (1887 – 1976) created problem-8, in order to prove that in chess compositions is not necessary only the power of the pieces but even their sacrifice in the suitable position. When we hit the target, no sacrifice is aimless.
The solution follows:
Key: 1.Rh5! (After the key the black king, which could initially take the knight Sg5, cannot move, but in exchange black can take the rook, which is considered stronger piece than the knight).
1...gxh5 (There goes the rook...)
2.Sh4+ Kxg5 (There goes the first knight...)
3.Bg7 Kxh4 (There goes the second knight...)
4.Bf6# (In three moves three white pieces are sacrificed, and then black is mated).


The positions of the legal problems should be reached, from the initial placement of the 32 pieces for a game, with a series of legal moves. If this is not true, then the position is called illegal and the problem is unacceptable.
Examples of illegal positions : White bishop on a1 and white pawn on b2 (how did the bishop go there?). Three white rooks and all eight white pawns on the chessboard (since no pawn is missing, which promotion produced the third rook?).


Characteristic 12 : The particularity. It is not readily seen what the key is.

	(Problem 9) Emmanuel Manolas, Newspaper "Peloponnissos", 07/04/1971, White plays and mates in 2 moves #2, retro, (9+3)
[8/8/P1Q5/KpP5/1P6/kB6/PS6/b5R1]

The problem-9 presents a difficulty for the unaware solver, who cannot spot readily the series of moves which mate black on the second move.
The problem needs retroanalysis, that is analysis of the moves which brought white and black pieces in the problem position.

The stipulation states that it is white’s turn to play. That means the black has just played his move. What was the move that black had just played?
The bishop Ba1 could not have played last. The king Ka3 could not have played last. Thus the black pawn (now on b5) had played last. From which square started to reach b5? Not from a6, not from c6, since there are white pieces there. Not from b6, because it was checking the king. Conclusion: the black pawn had moved last with double step from its initial position, b7-b5. That means that white has the right to take this pawn en-passant.
The solution follows:
Key: 1.cxb6 e.p. (The key is taking en-passant and with this move two lines of the queen are simultaneously open).
If 1...Bxb2 2.Qa4#
If 1...Kxb2 2.Qc1#

[This Post in Greek language]