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MatPlus.Net Forum General Rewan SE-inspired :-)
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(1) Posted by Hauke Reddmann [Wednesday, Dec 23, 2020 12:32]

Rewan SE-inspired :-)

Probably been done:

A position which is legal under different rotations of
the board (+-90° is allowed, ignoring b/w checkerboarding)
with unique but completely different retro.
5 second offhand example:
(= 2+5 )

(KxPg3; after 180° rotation PxXa8=B; too lazy to add black
pieces to make the victim unique; 90° not considered here(
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(2) Posted by Nikola Predrag [Wednesday, Dec 23, 2020 12:53]

1 second question: how wB has reached h1?
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(3) Posted by Joost de Heer [Wednesday, Dec 23, 2020 13:23]

Nikita Plaksin
7th HM Europe Echecs 1985
(= 9+14 )

Add the black king where he is mate
a) diagram
b) rotate 90 degrees clockwise
c) rotate 180 degrees clockwise
d) rotate 270 degrees clockwise
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(4) Posted by Hauke Reddmann [Wednesday, Dec 23, 2020 22:24]

@Nikola: Eeeeh...960? Didn't think it through until the final retro position :-) 2nd try:
(= 2+4 )

EDIT: Third idea:
(= 4+1 )

Zero: illegal
rot 90° right: dxc8R
rot 180°: hxg6
rot 90° left: O-O
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(5) Posted by Andrew Buchanan [Thursday, Dec 24, 2020 01:05]

Completing Hauke's third idea...

(= 5+1 )
Last move? (except we don't know what piece was captured (where))
b) rotation by pi/2
c) = b)^2
d) = b)^3

Note this specific configuration gives us at least the *possibility* of en passant to finish the Valladao.
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(6) Posted by Rewan Demontay (Real Name: James Malcom) [Thursday, Dec 24, 2020 01:50]

Andrew, for the en passant, try this cheat: e) +wLf1
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(7) Posted by Hauke Reddmann [Thursday, Dec 24, 2020 10:01]

Andrew, as I already said, it should suffice to add 8 black pawns
and 6 officers to make the captured piece unique (of course
we get no Valladao this way...). Placing the pawns such that the
structure is legal under all rotations is not completely trivial,
but since we have a whopping 11 white capture objects, this should be
possible by far. (Thus I assume it has been done before.)
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MatPlus.Net Forum General Rewan SE-inspired :-)