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MatPlus.Net Forum General "Pass Chess" - a new variant ?
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(1) Posted by Roddy McKay [Thursday, Apr 15, 2021 21:07]

"Pass Chess" - a new variant ?

Rules of “Pass Chess”

1. The board and pieces are as in “normal” chess.
2. Check, Checkmate and Stalemate are as usually defined.
3. A player may elect to Pass (make no move) at any time, which returns the move to the opponent, subject to 4. & 5. below
4. A player cannot respond to an opponent’s Pass with an immediate Pass.
5. A player who is in check, or has no legal move, cannot Pass.
6. There is no 50 move rule.

Though I haven’t composed any problems yet, I have been looking into the well-known examples of sufficient material to win against lone King, to try and establish whether they remain wins. These include :-
K + Q v K, K + R v K, K + B + B v K, K + B + S v K, K + S + S v K + P .
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(2) Posted by Jakob Leck [Thursday, Apr 15, 2021 21:57]

Welcome to the forum!

You might have some fun with pawn endings, as the rule you suggest seems to mess up the concept of zugzwang and, ensuing, opposition etc.
(= 2+1 )

1.Kc6 Pass? 2.d7+ Kd8 3.Pass!, 1.... Kd8 2.d7? Pass!, 1.... Kd8 2.Pass! Kc8 3.d7+ etc.
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(3) Posted by edderiofer [Friday, Apr 16, 2021 05:28]


I'm not very experienced with problems, but my gut instinct is that this will give less variety in problems due to the lack of zugzwang in forwardmates, retrostalemate in retros, and tempo moves in proof games. I suppose there could be more interesting ideas that come up in endgame studies or helpmates, though.

Then again, like I said, I'm not very experienced with problems, so I could be talking nonsense here.
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(4) Posted by Hauke Reddmann [Friday, Apr 16, 2021 17:57]

KQ/K is obviously won. White can check the K back.
KR/K seems drawn. Black passes on any, or walks
out of opposition.
KBB/K seems drawn either, even more so KBN/K.

In general, since Black can pass on any further
move, only endgames are won where Black can be
checked to kingdome come. KRR/K, K+3 light/K.

Pawn endgames will be interesting.

Of course, tablebases should be rather easily
adaptable to the pass move.
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(5) Posted by Ulrich Voigt [Friday, Apr 16, 2021 20:18]

I'm pretty sure K+R vs K is still won. The king can be forced towards the border step by step. Let's start with this position:

(= 2+1 )

1. Re7 pass 2. Rf7 Ke4 3. pass Kd4 4. Rf4+, and the king is forced to leave the center. Again, White positions his rook so that the Black king is restricted to the smallest possible rectangle, and repeats the same maneuver:

(= 2+1 )

1. Re6 pass 2. Rf6 etc.

Rinse and repeat; the King can't escape the border. Finally:

(= 2+1 )

1. Rd2+ Ke1 2. pass Kf1 3. Re2 pass 4. Ke3 pass 5. Kf3 pass 6. Re4 pass 7. Rd4 Kg1 8. Rd1+ Kh2 9. pass, or 7... Ke1 8. pass.
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(6) Posted by Hauke Reddmann [Saturday, Apr 17, 2021 11:23]

Ah, I see. White passes so that Black can't. (Still, this only works because R+ is a threat, forcing Black to not pass.) "You shall not pass!" Sorry. :-)
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(7) Posted by Roddy McKay [Sunday, Apr 18, 2021 12:14]

K + B + B is probably a win, e.g. Kf4, Be4, Bd4, kd6 when white can manoeuvre his king to e4 then maybe d4 bishops to c5 and d5 so black has moved one rank nearer to the edge. Repeat and black king will be on the edge where mate is possible. Black passing won't save him.

K + B + S is difficult, and may not be a win. The traditional defensive strategy of retreating to a corner of opposite colour to the Bishop is insufficient e.g. Kf6, Sf7, Bd3, kg8 where Black has just passed. In "normal" chess the game would continue e.g. Be4 Kf8 Bh7 etc. But in Pass Chess White has Sh6+ Kh8 Sf7+ Kg8 Pass Kf8 Bh7 reaching the same position.....
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(8) Posted by Hauke Reddmann [Monday, Apr 19, 2021 13:00]

@Roddy: looks legit. (It's definitely different from the
standard KBB/K mating strategy.)
KSB/K *might* work. Blacks best strategy is run for the
hills, passing doesn't help. But assume Kf6 Bf5 Sf7/Kg8.
How to smoke the K out of the wrong corner? A check
is required, but the wS has to cover h8. So my best bet
is "impossible against correct play".
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(9) Posted by Ulrich Voigt [Monday, Apr 19, 2021 16:27]

I'm not convinced yet - either way.

Let's say the king made it to the wrong corner and refuses to come out. White can reach this position:

(= 3+1 )

1. Nh6+ Kh8 2. Nf7+ Kg8 3. pass Kf8 4. Bh7 pass 5. Ne5 pass 6. Nd7+ Ke8 7. Ke6, and White made a lot of progress.
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(10) Posted by Hauke Reddmann [Monday, Apr 19, 2021 23:01]

In that case I'd go to f8 from the check, as the S stands silly.
But again I underestimated your strategy "Check to pass yourself
if necessary", and I agree the jury is hung and a tablebase
should solve it for good. (Also, Deletang method exists.)

Maybe Noam Elkies could construct us a tis|tisn value* in the
corner which more or less could allow to feed the position
in a standard engine...
* From the "Winning Ways for your Mathematical Plays" book

(= 2+16 )

Black has infinitely many pass moves, White none, also interesting
(EDIT: KBB/K still seems won, but not KR/K)
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(11) Posted by Rewan Demontay (Real Name: James Malcom) [Tuesday, Apr 20, 2021 05:17]

I'm pretty sure KRR-K is impossible to win. I remembered an old post, third one down, by Geoff Chandler in 2011 in the English Chess Forum that I think proves i:

I shall quote the relevant section.

"A Lucky Escape in the Rules.

When the original rules were being laid down some bright spark might have
added that when a player is left with a lone King he can 'pass' and give the
move back to his opponent."

(= 2+1 )

If so then it would impossible to deliver mate in a King & Rook v King ending.
From the above position.

1.Rc2 pass
2.Rc3 pass
3.Rc1 pass
4.Rh1 Kc8"
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(12) Posted by Hauke Reddmann [Tuesday, Apr 20, 2021 09:30]

Have to add a small correction: tis|tisn tisn't :-)
So we now have at least three playable definitions
of chess including pass moves:

1. The one given at the top of this thread.
2. on|off pass: Any side may pass at any time
(unless checked or stalemated, as usual)
3. tis|tisn pass: Any side may pass by handing
the pass key to the opponent. In any starting
position Black will have the key. (I.e., you
can't pass twice without the opponent passing.)
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(13) Posted by Joost de Heer [Tuesday, Apr 20, 2021 09:52]

Kb6 Rc1 / Kb8

1. Rd1 Kc8 2. pass Kb8 3. Rd8#

Or am I missing something?
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(14) Posted by Frank Richter [Tuesday, Apr 20, 2021 10:46]

Why not 1.pass Ka8 2.Rc8# ?
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(15) Posted by Hauke Reddmann [Tuesday, Apr 20, 2021 11:37]

No, no, you are both right: The key to winning KR/K in
the *thread* variant is to threaten a check, so that
Black can't pass, and then pass yourself, so Black again
can't pass, and is driven back. This strategy doesn't
work in the pass-whenever-you-like (on) variant. Or as a table
("ko" means the thread variant, by analogy to the Go rule):

ko + + + ?
tis + + + +
on + + = =
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(16) Posted by Andrew Buchanan [Tuesday, Apr 20, 2021 17:55]

In Pass Chess, with the trebuchet, if one player tries to put the other in Zugzwang, then the other passes and may then win, as the opponent is in real ZZ. The key to drawing KPvK in this new version as the bare king is to occupy the pawn promotion square, because one can no longer be pushed off it.
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(17) Posted by Geir Sune Tallaksen Østmoe [Thursday, Apr 22, 2021 00:30]

Interesting discussions! I suspect KBN-K is a draw, but I am not sure.

(= 3+1 )

With the bishop on f5 instead of e4, I think 1.Nh6+ Kf8 is met simply by 2.pass Ke8 3.Nf7, and we are back in well-known territory.

However, I don't see how to make progress after the standard sequence 1.Nh6+ Kh8 2.Nf7+ Kg8 3.pass Kf8 4.Bh7 Ke8 5.Ne5 Kd8 6.Ke6 Kc7 7.Nd7 Kc6 8.Bd3 and now 8...pass! Now Black just passes every move until White gives up b5 or c5.

(= 3+1 )

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(18) Posted by Hauke Reddmann [Thursday, Apr 22, 2021 15:34]

Note that even in KR/K Black can put up a bit more
resistance than implied by Ulrich. Assume we have
Ke4 Rc3 - Kd6 and White can't pass. The trick is,
as always, checking:
a) 1...Kc5 2.Rc3+ Kd6 (otherwise Black has been
driven out of ring 2 immediately) 3.pass,
b) 1...Ke6 2.Rc3 Kf6 3.Rc6+ Kg5 3.pass.
But what to do if we move the position one row
upwards? Black would escape to c6.
The cage method seems to be more effective, assume
Ke5 Re6 - Ke7, which is easy to obtain. Now on e.g.
1...Kd7 2.pass Kc7 3.Rd6.
Now we can switch back to the first method, after
which Black lands on the border.

I *really* think tablebasing it would be helpful ;-)
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(19) Posted by Kevin Begley [Wednesday, Apr 28, 2021 18:11]

Smart variant idea!
As others have noted, it would definitely be interesting to explore what an EGTB in this variant might yield -- especially if KBNk proves a win, based upon some shrewd (and overlooked) pass strategy!

That's how you know a variant is good:
1) it's simple to describe the rules,
2) the rules flow naturally (nothing is arbitrary), and
3) (best of all) it leaves enthusiasts pondering the optimal results of various endgames.

I suspect an EGTB will yield some rather surprising conclusions, though I wouldn't bet on a win in KBNk.
I hope somebody will write an article exploring what interesting results this variant's EGTB might yield (and make it available here).

It would also be interesting to see problems where the solution requires a smart pass strategy (especially helpmates which require passing from both sides).
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(20) Posted by seetharaman kalyan [Wednesday, Apr 28, 2021 19:28]

Welcome back Kevin Begley
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MatPlus.Net Forum General "Pass Chess" - a new variant ?