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MatPlus.Net Forum General Helpmate...under rapid rules :-)
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(1) Posted by Hauke Reddmann [Monday, Aug 6, 2018 11:47]

Helpmate...under rapid rules :-)

(= 3+1 )

h#1.5, 3 solutions

1.Qb4 Kc4!! 2.Td4#!!!
(In helpmate, White and Black work together. If Black makes an illegal move,
White is not obliged to call the arbiter. Which is nonexistent anyway :-)

Hauke, in troll mode
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(2) Posted by Nikola Predrag [Monday, Aug 6, 2018 12:28]

Only 3 solutions? What about 1...Qe6 2.Ke5 Re4#?
And what about e.g. 1...Rh6 2.Kg5 Rg6#, or dual mate in 1...Kg1 2.Kh1 Kf2/f1 #?
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(3) Posted by Siegfried Hornecker [Monday, Aug 6, 2018 13:29]

My favorite solution is 1.-0-0-0 2.Kd8 Qd7 mate. This has dual avoidance, as the mating move must be legal (so 1.-Qd7 2.Kd8 0-0-0 mate does not work).

Trolling the troll,
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(4) Posted by Hauke Reddmann [Wednesday, Aug 8, 2018 08:04]

@Nikola: You're right, of course. Evidently, we have to define
"slightly" and "very" illegal moves first before we can formalize
the new fairy condition :-)
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(5) Posted by Geir Sune Tallaksen Østmoe [Wednesday, Aug 8, 2018 09:34]

There is also 1.Rc6 Q@e5 2.Qc4#. @ means Black puts his queen, which was captured earlier, back on e5.
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(6) Posted by Andrew Buchanan [Tuesday, Aug 28, 2018 19:16]; edited by Andrew Buchanan [18-08-28]

White begins by "moving" to any position. Assuming we avoid draughts, Cluedo suspects, lego, candies etc, that means any of 13^64 mappings of the 64 squares onto the 13 possible contents (KQRBSPkqrbsp-). He does not have to worry whether Black is checkmated, stalemated or in dead position, because the final move in the game must be legal. E.g. even if he rearranges the pieces so that Black appears to be mated, it is not actually checkmate so Black is now free to play an illegal move. There are no short mates in this problem. Black has the responsibility to tidy up the board a little: so that there is exactly 1 black king (64x12^63 positions) and moreover at least one legal White mating move must exist. White proceeds to execute this, with solemn sang froid appropriate to the legality of this final play. Sublime composition, thank you.
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(7) Posted by seetharaman kalyan [Wednesday, Aug 29, 2018 19:38]; edited by seetharaman kalyan [18-08-29]

I suppose that after 1.Kc4 white simply takes the king !! 2.Rd4# simply results in an illegal mate position.
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(8) Posted by Hauke Reddmann [Thursday, Aug 30, 2018 11:40]

But under FIDE rules, capturing the king is ille...
OK, point taken :-)

Hmmm...would it be possible at all to codify what is a "legal illegal" move?
One could, sorted by evilness...
- Ignore retroillegality of ep or OO
- Ignore checks (where castling out or through a check would be less illegal :-)
- Make a "move" that isn't possible, including setting up the board ad lib
- Play Calvinball
- Pull out a gun and shoot the opponent :-)))

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(9) Posted by Joost de Heer [Friday, Aug 31, 2018 08:34]; edited by Joost de Heer [18-08-31]


2.Rd4# simply results in an illegal mate position.

The mate position is legal, the move leading to it is legal too under the rapid rules. So where does your 'illegal mate position' come from?

The relevant article:

If the arbiter observes an action taken under Article 7.5.1, 7.5.2, 7.5.3 or 7.5.4, he shall act according to Article 7.5.5, provided the opponent has not made his next move. If the arbiter does not intervene, the opponent is entitled to claim, provided the opponent has not made his next move. If the opponent does not claim and the arbiter does not intervene, the illegal move shall stand and the game shall continue. Once the opponent has made his next move, an illegal move cannot be corrected unless this is agreed by the players without intervention of the arbiter.

If I understand this correctly:
- Black plays Kc4, an illegal move.
- White doesn't claim and plays 2. Rd4#, thereby removing the illegality of the previous move ('... the illegal move shall stand and the game shall continue ...'). If Kc4 is accepted, 2. Rd4# is a perfectly legal move.


I suppose that after 1.Kc4 white simply takes the king !!

Capturing the king is still an illegal move, and not a win (the black king isn't mated, it's captured, so the goal of the game, to mate the opponent's king, isn't met). Actually, if white captures the king, the game is an immediate draw (black has no legal move left and isn't in check, so it's a stalemate), unless black claims the illegality of the capture.
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MatPlus.Net Forum General Helpmate...under rapid rules :-)