Spartan chess, promotion to king

[TonyJH]

With white to move in this position, does Qg5 result in checkmate, or can black then play e2d1=K? I thought this would be checkmate, but WinBoard did not consider it checkmate.

8/7h/4NQ2/P6k/2h5/8/4h2P/1K6 w - - 0 46
[d]8/7p/4NQ2/P6k/2p5/8/4p2P/1K6 w - - 0 46

There was a similar position posted here , but in that case it was black to move, so it definitely made sense that black could promote to king to avoid mate.

[Ferdy]

With white to move in this position, does Qg5 result in checkmate, or can black then play e2d1=K? I thought this would be checkmate, but WinBoard did not consider it checkmate.

8/7h/4NQ2/P6k/2h5/8/4h2P/1K6 w - - 0 46
[d]8/7p/4NQ2/P6k/2p5/8/4p2P/1K6 w - - 0 46

There was a similar position posted here , but in that case it was black to move, so it definitely made sense that black could promote to king to avoid mate.

I tend to think this way, if white played Qg5, then black should be given a chance to make a move. Now if black promotes to another king then there is no mate.

[Evert]

Look at it this way: if you are in check, then your objective is to make sure that you are not in check after making a move.
After 1. Qg5, black is in check. After 1. ... d1K, black is not in check. Hence, it's a legal move.

[TonyJH]

I agree, what both of you said makes sense. It's a little unclear to me from reading the official rules:

The Persian wins once one of the Spartan Kings is captured and the remaining Spartan King is checkmated or when both Spartan Kings are placed under simultaneous attack (duple-check) and neither King can be removed from attack on the next move (see 4.4 Duple-Check and Mate).

Since the condition in bold is met in this position after Qg5, from one point of view: One of the kings was already captured and the remaining king is 'checkmated', which I originally interpreted as meaning just that king himself cannot get out of check.

[Vinvin]

In fact, the condition in bold seems illogical and could mean : Even if you have already promote a new king, The Persian wins once the remaining (the one who started the game and was not taken) Spartan King is checkmated.

I agree, what both of you said makes sense. It's a little unclear to me from reading the official rules:

The Persian wins once one of the Spartan Kings is captured and the remaining Spartan King is checkmated or when both Spartan Kings are placed under simultaneous attack (duple-check) and neither King can be removed from attack on the next move (see 4.4 Duple-Check and Mate).

Since the condition in bold is met in this position after Qg5, from one point of view: One of the kings was already captured and the remaining king is 'checkmated', which I originally interpreted as meaning just that king himself cannot get out of check.

[Ferdy]

I agree, what both of you said makes sense. It's a little unclear to me from reading the official rules:

The Persian wins once one of the Spartan Kings is captured and the remaining Spartan King is checkmated or when both Spartan Kings are placed under simultaneous attack (duple-check) and neither King can be removed from attack on the next move (see 4.4 Duple-Check and Mate).

Since the condition in bold is met in this position after Qg5, from one point of view: One of the kings was already captured and the remaining king is 'checkmated', which I originally interpreted as meaning just that king himself cannot get out of check.

That document could be improved, and I suggest to clarify those rules by giving more examples. Let's wait for HGM's ideas.

[hgm]

Indeed, promoting to King is a valid way to evade check. (But Fairy-Max, not supporting under-promotions, does not know that, and thus occasionally sees phantom mates. I suppressed the mate claim in Spartan Chess in such cases (Hoplite on 2nd rank) to prevent an immediate loss.)

The document is unclear, and especially the terminology 'when your King is checkmated' is objectionable. Kings are not checkmated, players are. Checkmate is when you are in check, and cannot get out of it by any pseudo-legal move. That is a property of the entire position, not just of the King.

In Spartan Chess 'check' is defined as 'all your Kings being under attack'. When you have one King that is not under attack you are not in check (i.e. not under any obligation to do something about it). So the under-promotion to King resolves the check in the given position after Qg5+, and hence you are not checkmated.

[George Tsavdaris]

In Spartan Chess 'check' is defined as 'all your Kings being under attack'. When you have one King that is not under attack you are not in check (i.e. not under any obligation to do something about it). So the under-promotion to King resolves the check in the given position after Qg5+, and hence you are not checkmated.

Yes but perhaps checkmate is supposed to have a higher precedence than promoting, like in Chess checkmate has a higher precedence than 50-move rule (so if you play a move that will end up in both players to have completed 50 moves without any Pawn movement or piece captures but you checkmated your opponent, the opponent can't ask for 50 move rule to apply and he is checkmated).

It's all about what checkmate position means, so it's a matter of definition so there is no real point of arguing about what is correct and what is not because nothing is correct. Only the inventor of Spartan Chess can define what checkmate means for his game for the Persians so he should clarify.

Your definition of checkmate as not having any move(legal of course) that can throw your only King out of check is the best i think and makes the underpromotion here a valid move to continue the game, but perhaps the inventor of Spartan Chess will define checkmate as a position where the remaining King is under attack and can't escape from the attack without still being in check.
The second definition applies the logic(philosophy) of Chess(of 1 King), while yours applies the logic of Spartan Chess(where Spartans have 2 Kings so even if one is lost the other can still be the King).

[hgm]

Formally you are right, but as all engines that play Spartan Chess are WinBoard engines, the most important thing in parctice is how WinBoard implements this.

But I think I discussed this with the inventor, and the WB implementation has its full approval.

I admit that sometimes designers solve ambiguities in their rules in a very illogical way. In Seirawan Chess, for instance, in the position below you would not be allowed to play Nh3/E (gating in an Elephant on g1):

[d]rnb1kbnr/ppp1pppp/8/3p4/8/4P3/PPPPBPP1/RNBQK1Nq w

The 'explanation' is that you would be in check after the Knight evacuated f1, but before you put the Elephant there. So the move is really seen as a two-step move, the second step (dropping the Elephant) being subject to a veto, somewhat like e.p. capture.

[TonyJH]

Thanks for all the replies. Changing the topic a little bit:
I was looking at some endgame scenarios for Spartan chess, and these all seem to be winnable for black (in general). I suspect they are forced wins.
kc-K: king and 1 captain vs king (interesting since the captain is just a minor piece)
kll-K: king and 2 lieutenants vs king
kk-K: 2 kings vs 1 king

I saw that WinBoard 4.5.3 adjudicated kll vs K as a draw (insufficient material), so I had to turn adjudications off to test that one.