Julia's Fairies

No.737 (OS)

Oliver Sick


Original Problems, Julia’s Fairies – 2015 (I): January – June

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No.737 by Oliver Sick – Wormhole condition with specific e.p. capture. To my opinion, the logic of this solution is debatable, however it is C+ by Popeye. Still, the animation by Py2Web seem to be impossible for such e.p. capture. I’d appreciate reader’s comments! (JV)


Wormhole (sent by author): Wormhole is property of the squares. If a move of the piece ends on a wormhole, the piece is transferred to any other unoccupied wormhole. A pawn moving to a promotional square, which is a wormhole itself, promotes and the promoted pawn is transferred to another wormhole. If a pawn is transferred to its ground row, it can make a single step or capture. If a pawn makes a double step onto a wormhole, it still can be captured en passant, even if the pawn has been promoted into any figure. Zero moves are not allowed. (translation of the definition from Die Schwalbe)

Circe: Captured units (not Ks) reappear on their game-array squares, of the same colour in the case of pieces, on the file of capture in the case of pawns, and on the promotion square of the file of capture in the case of fairy pieces. If the rebirth square is occupied the capture is normal.

No.737 Oliver Sick

original – 27.02.2015

Solution: (click to show/hide)

neutral Pc4 black Kf5 white Pd2 Ke1

h#1,5                                       (2+1+1)
Wormholes d3, d4, g1, g8

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Vlaicu Crisan
Vlaicu Crisan
February 28, 2015 10:32

Can somebody from Popeye team answer to the following questions:
1. Why the neutral pawn played by Black on the 8th rank is promoted into a neutral Queen? I think neutral pawns played by Black can promote still only on the 1st rank.
2. Why the short castling is allowed, although the [intermediate] square g1 is under the observation of the neutral Queen?
Please also let us know if you consider the above mentioned behaviors as features or bugs. Thank you very much!

February 28, 2015 12:02
Reply to  Vlaicu Crisan

Hello Vlaicu,

I am not part of the popeye team. But I see the following :

On 1.:
The definition of neutral pawns is that they promote on the 1st or 8th rank. The rules for neutral pawns I know (from the net or chess magazines) say nothing about the party who is promoting the pawn (=> promotion on g8 is allowed ?!?) Popeye 4.69 uses this definition consequently (eg. also for supercirce…)

On 2.:
The square g1 is attacked in deed, but only when a moves ends on it. In this case the move ends on d4. But in fact I also feel uncomfortable with this, because of the following observation in Popeye 4.69:

Castling is now allowed in the following situation
Condition Wormholes d4f1
white Ke1 Rh1
black Qf8 Ke6

but is allowed here
Condition Wormholes d4g1
white Ke1 Rh1
black Qg8 Ke6

This feels ambigous (what is the difference between f1 and g1?!?). Of course to avoid this ambiguity I could add a bPg4, but I’ve looked for a minimal….

Kjell Widlert
Kjell Widlert
February 28, 2015 12:01

(I’m not in the Popeye team, so these are just my personal thoughts.)

Q1. The Q promotion on g8 looks to me like a bug. It is indeed Black who plays the P to his own first row, which by the wormhole rules should imply that it stays a P, being able to make a single-step or a capture from there.
(But on the other hand: How are neutral Ps in other fairy forms – PWC, Einstein or some other – treated when they appear on row 1 or 8? You could argue that on the following half-move, the nP is on the promotion rank of that side, and why then is it not promoted?)

Q2. This seems to me like a feature! g1 is not the intermediate square in the castling (that would be f1). A king can move to a guarded (observed) wormhole if he is then transported to another, unguarded wormhole. That should be legal also when the king moves onto the wormhole by castling.
(The follow-up question is harder; what if f1 is a wormhole, is castling legal or illegal? Does it depend on whether there is another unguarded wormhole or not (i.e., whether a direct K move to f1 would be legal or not)?

Georgy Evseev
Georgy Evseev
February 28, 2015 14:40
Reply to  Kjell Widlert

I would say that castling is illegal.

FIDE rules:
Castling is prevented temporarily if the square on which the king stands, or the square which it must cross, or the square which it is to occupy, is attacked by one or more of the opponent’s pieces

So, white king is not allowed to visit g1 during castling.

Kjell Widlert
Kjell Widlert
February 28, 2015 15:58
Reply to  Georgy Evseev

But the king is not going to occupy g1 … but d4!

Laco Packa
Laco Packa
February 28, 2015 22:20
Reply to  Kjell Widlert

Such explanation is, of course, possible. It is then necessary to consider the fact that the pawn did not move on d4 , but g8 – is then e.p. possible?

Vlaicu Crisan
Vlaicu Crisan
February 28, 2015 22:40
Reply to  Kjell Widlert

Kjell, I agree with you the king is not going to occupy g1. But does it cross that square during the castling?

Geoff Foster
Geoff Foster
February 28, 2015 22:43
Reply to  Vlaicu Crisan

There is a bug in Popeye whereby neutral pawns can promote on their own first rank. The bug was introduced in version 4.63. For more details see:
156 Neutral Pawns can promote on home rank

Kjell Widlert
Kjell Widlert
March 1, 2015 13:09
Reply to  Geoff Foster

What should happen to a neutral pawn brought to the 1st or 8th row is at least debatable. After all, a neutral pawn is both white and black at the same time, so “their own first rank” is not a clearly defined concept.

One option is to let the role of the nP when it gets to the first or last rank decide what happens: if a nP is treated as white when it gets to row 8 (i.e., played by White or captured by Black), then it promotes; if it is treated as black when it gets to row 8, then it stays as a nP – mobile for Black but immobile for White.

But another option is to simply say that both row 1 and row 8 are promotion ranks for neutral pawns (as they are both black and white), no matter how the nP gets there.

Cornel Pacurar
March 1, 2015 17:11
Reply to  Kjell Widlert

As far as I know, until Popeye v4.63, the first option described above was the only option considered by both programmers and chess problem composers (there are tens of such compositions). This is aligned with T.R.D’s view on neutrals: “neutral pieces […] may be played by either player – moved if he regards them as his own, or captured if he regards them as adverse” (Caissa’s Wild Roses). When moved or captured they are regarded as ‘either’ white or black but not as ‘both’ white and black at the same time – in the end, they are ‘neutrals’ not ‘grey’. So, if neutral pawns are regarded as white or, respectively, black, at the beginning of the move, they should not be regarded as black or, respectively, white, at the end of the move. I personalty find the fact that the behaviour was changed starting with Popeye v4.63 (ironically, when Wormholes was implemented) disregarding definition, precedent and without being formally announced, as unfortunate.

March 1, 2015 22:00
Reply to  Cornel Pacurar

WinChloe seems to disallow the possibility, for a nP moved by the white side, to reach the first row.
As an example with nPc4 bBd5 in T&M, cxd5 with make move to a8 or g8 is legal, but make move to h1 is illegal.

Maybe such a simple and logic rule should be kept without T&M, but instead with a couple of wormholes (d5,h1). In that case maybe the capture cxd5 should be declared illegal.

March 1, 2015 03:42
Reply to  Kjell Widlert

With wKe1 wRh1 and wormholes on f1 and d4, Popeye allows 0-0 but without the additional Rf1->d4. If we put the wormhole f1 on g1, Popeye still allows 0-0 but with the additional Kg1->d4.

To my eyes the underlying logic is correct here, if we remember that 0-0 is only a King move. In particular the involved Rook doesn’t “move” to f1 during the castling procedure, it is “transferred” to this square – a kind or rebirth.

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