Fairy chess composition
 No.1279 Paul Rãican (Romania) Original Retro & PG problems JF – R2017-18

Definitions sent by the author: (click to show/hide)

 No.1279 Paul Rãican Romania original – 25.02.2018 Solution: (click to show/hide) white Oa1b1c1d1e1f1h1a2b2c2d2e2h2g3g4g5e6g6h6a7b7d7e7f7g7a8c8d8e8f8g8h8 PG 5    White is checkmate    (x+y=32) Undefined pieces Annan Chess 960 (no animation for Undefined pieces (JV)) (RQSBBKRS) 1.g2-g6 c7-e6 2.h2-g4 Qh2 3.f2-g3 Qh6 4.0-0! 0-0! 5.Kh2 h7-g5# (5. ...h7-f6+? 6.d2xh6! and 5. ...f7xf1=S+? 6.e2xf1!) Jacobi+ in ~34 h Indian theme, castlings. (Author)

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seetharaman
February 25, 2018 18:23

hm… so, what was the starting position? How is it arrived at?

François Labelle
February 25, 2018 20:01

In a Chess960 PG, the starting position is part of the mystery. It must be found through retrograde analysis (or through trial and error).

This particular problem seems to be missing the condition “Checkmate position”, though. The are many cooks without it.

seetharaman
February 25, 2018 20:33

Thanks. That is what I understood too. What I meant was why the starting position is not mentioned in the solution and why there is no explanation in the solution how that starting position was arrived eliminating other positions.

François Labelle
February 25, 2018 21:12

The first rank of the starting position was given just before the first move of the solution, you probably missed it. As for your other point, in an ordinary PG the move sequence of the solution is arrived at by eliminating other potential move sequences, but in the comment section of other PGs I don’t see you commenting that there is no explanation in the solution how the move sequence was arrived at. Why should it be different here, replacing “move sequence” with “starting position”?

Seetharaman
February 26, 2018 18:54

Sorry I missed that the starting position is mentioned in the solution.

François Labelle
February 25, 2018 22:18

Much better! Now I wonder about the relevance of the alternate moves (5. …) discussed in the solution, because they don’t even obey the diagram with undefined pieces. They would make sense if the stipulation were “PG 4.5 & #1”, but not when it’s “PG 5 white is checkmate”, right?

Paul Rãican
February 25, 2018 23:46

A demolished version of this enigma took part in the Quartz TT10. Only after Jacobi was launched was it possible to get it sound. Thank you, Francois! And thank you for all the comments that help to understand this puzzle. The alternative moves B5 makes sense, indeed, if the stipulation were PG4.5 then #1. I wanted to show only that the mating move is unique, for the giving position.

Nikola Predrag
February 25, 2018 22:15

Well François, looking for possible n-moves and possible n-moves x 960 is not the same thing (unless n=0 -:)).

François Labelle
February 25, 2018 22:44

They’re not, but the difference is the same as adding one extra move. Chess960 could be defined as a fairy condition that starts orthodox, followed by “move 0” which is a special move where we shuffle the pieces to one of the allowed 960 start positions, followed by ordinary chess moves. With that point of view the entire solution is a sequence of moves, and so there is no reason to worry about move 0 and not about move 1 or move 2. The written solution even looks like that interpretation.

Georgy Evseev
February 26, 2018 11:35

Does Jacobi+ means that all 960 possible initial positions were checked and there is no solution in other 959 cases?

Paul Rãican
February 26, 2018 16:22