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MatPlus.Net Forum General SAT
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(1) Posted by Joost de Heer [Wednesday, Dec 2, 2020 20:09]


Definition from Julia's Fairies:
A King is under check if it can move to only one square not controlled by the opposite side.

Definition from Die Schwalbe:
SAT = Salai-Matt: Ein König gilt als im Schach stehend, wenn er im orthodoxen Sinne ein oder mehrere Fluchtfeld(er) hat.
[Translation: A king is under check if he has, in the orthodox sense, one or more flight squares.

So 'only one' vs 'one or more'. What is the correct definition?
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(2) Posted by Juraj Lörinc [Wednesday, Dec 2, 2020 22:29]

One or more. There were various variants tried and used even by the inventor, until this has settled as the most useful definition.
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(3) Posted by Andrew Buchanan [Thursday, Dec 3, 2020 06:45]

This pattern of convergence to a standard definition is interesting from a taxonomic perspective. Bosma is another case where some early problems had different assumptions. Also an engine designer is often obliged to specify an interpretation for each condition, even universal agreement does not exist. Problems need to be properly keyworded to protect them from being incorrectly marked C-, which would be a slur on the composer, often no longer with us. This is all about handling corner-cases cleanly while avoiding losing overall coherence.
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(4) Posted by Hauke Reddmann [Thursday, Dec 3, 2020 11:54]

<troll mode> Orthodox Chess is exactly the fairy chess variant to which it converged :P
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(5) Posted by Neal Turner [Thursday, Dec 3, 2020 13:54]

Yes, the definition on Julia's site is unfortunate.
Not only is it incorrect with the 'only one' business, but it's also incomplete with the 'can move' part.
What should made explicit is that it 'can move' under orthodox (or other specified fairy) rules.
All this business with the moving is very confusing - elsewhere I've attempted come up with a form of words that didn't refer to possible king moves.

If we define flight squares are those squares in the king's field which are not blocked we can say:
"The king is in check if any flight square is not guarded by an opposing piece."

I even put forward the idea that SAT shouldn't be thought of as a fairy condition at all, but as a definition of a type of fairy king.
- Orthodox king: in check when its own square is attacked
- Anti-king: in check when its own square is not attacked
- SAT king: in check when any of its flight squares is not attacked
But this was considered too radical.
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(6) Posted by Frank Richter [Thursday, Dec 3, 2020 14:11]

By the way ... last week I saw a german crime movie called "The Pinned King".
Is there any fairy condition, that would be allow to pin a (orthodox) king?
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(7) Posted by Sarah Hornecker [Thursday, Dec 3, 2020 14:13]

Isardam can be used to pin a king, but you must use fairy pieces also, so the king himself is not threatened but if he moves the two fairy pieces threaten each other.

EDIT: I wrote something stupid here. Of course the "capture" is illegal with normal pieces also if they would attack each other after capturing the king, thus there is no check and the king can be pinned.
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(8) Posted by Hauke Reddmann [Thursday, Dec 3, 2020 14:24]

@Frank: Still on my watch-and-write-snide-review list,
no THX at all for reminding me :-)
(To all readers here: German crime procedural series,
pinned/gefesselt is to be understood literally, the
corpse was found in bondage. Bother, that was the
wrong word again. :-)
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(9) Posted by Neal Turner [Thursday, Dec 3, 2020 14:46]

Of course in SAT, if its own square was wasn't attacked, then the king would be pinned as any move would be self-check on its departure square.
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(10) Posted by Frank Richter [Thursday, Dec 3, 2020 15:13]

@Hauke: You surely understand, that this title is to understand ambiguously ...
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(11) Posted by Andrew Buchanan [Thursday, Dec 3, 2020 15:30]

The Encyclopedia has:


Fairy condition. A side is checked if its King can
move according to other (orthodox or other given
fairy) rules. (Logically, a side to move is checkmated
if it is checked and it cannot parry the
check by its own move.)

Sharp SAT: A side is checked if its King has at
least one flight. (Logically, a side to move is
checkmated if it is checked and it cannot parry
the check by its own move.) Beginning with the
first attack of King by an enemy unit, the square
occupied by King is considered to be his flight
when this square isn't attacked.
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(12) Posted by Neal Turner [Thursday, Dec 3, 2020 15:51]

Now we can see why SAT isn't very popular!
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(13) Posted by James Malcom [Thursday, Dec 3, 2020 16:07]

Frank, I'm not sure if exactly counts, but Bosma+Rex Multiplex does the job, simply and just cleanly.

Here's a semi-conplica†ed try at it. There'll be no surprises if it's cooked.

=3, Bosma+Rex Multiplex
(= 9+4 )

1. Rxb2+! Kd5 2. Ne4+ gxh5 3. Kh4=

In normal RM, you can't check two kings at once, thus you can't pin them either. But with Bosma, a pinned king be forced to move into a triple attack in order to relieve its counterpart. Or, at the least, that's how I perceive it.

Funnily enough, this makes it illegal to relieve the triple check in some cases. This seems to stalemate then, here down below! Neither bishop nor king is allowed to move without self-check.

(= 7+4 )

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(14) Posted by Guus Rol [Friday, Dec 4, 2020 11:52]

@RewanDemontay: I played a while with Bosma myself though I didn't produce any published problems with it. The issues are the same as with "Ohne schach" and similar types. The first question is always whether or not orthodox mates are mates. It's an independent decision like "Rex inclusive" or "Rex exclusive" in other types. I dont know what the current default is for Bosma but there is no harm in introducing 2 different flavours for "OMate inclusive" and "OMate exclusive" (referring to orthodox mate) in these fairy dimensions. Probably somebody already defined those. Orthodox in this context does not refer to orthodox chess rules but to an orthodox evaluation function. Equihoppers can participate in an orthodox Bosma mate but mates dependent on the Bosma condtion can not.

In itself there is no difference between the Bosma/OhneSchach dimension in an orthodox chess problem and a fairy chess problem (like multiple black kings). When you are sure of the operation of your fairy rules then you should be capable of deciding on the effects of the "OMate inclusive" and "OMate exclusive" operators on your solutions.
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(15) Posted by Marjan Kovačević [Friday, Dec 4, 2020 18:41]

@ Neal, Andrew & Joost
A huge JF project is going on to add some light and order in the jungle of fairy elements:
Till now, the project has been supported by only a small number of optimistic problemists ready to help.
For those who were pessimistic about the whole project, correcting the SAT definition is a concrete chance to take part and see the results, since the list of terms and definitions became open for everybody to contribute:
Joost gave a comment about SAT definition on JF, and the administrator accepted it, but now it seems the new definition should be completed.
What you could do is to write correct definition in the comment field, and it would be inserted by the admin.
Otherwise, all this discussion would be useless and quickly forgotten.
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MatPlus.Net Forum General SAT