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MatPlus.Net Forum Retro/Math Castling
 
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(21) Posted by Jacques Rotenberg [Sunday, Oct 31, 2021 10:01]

perhaps this ?

(= 2+13 )


a)
- If the rook moved last, 1. Rxh2[Ra1] 2. Rxa6[Rh1] 3. 00
- If the king moved last, 1. Ke2 2. Kxf3[Ke1] 3. 00
b)
We don't know which piece moved last, 1. Rg1 2. Rxg3[Ra1] 3. Kxf2[Ke1] 4. 000

it is even lighter
 
   
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(22) Posted by Jacques Rotenberg [Monday, Nov 1, 2021 01:54]

I would even prefer like this :

(= 2+13 )

ser-castling in how many moves? Anticirce

- If the rook moved last, 1. Rxh3[Ra1] 2. 00
- If the king moved last, 1. Ke2 2. Kxf3[Ke1] 3. 00
- If last move not known, 1. Rg1 2. Rxg3[Ra1] 3. Kxf2[Ke1] 4. 000

but... it does not work!
 
   
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(23) Posted by Jacques Rotenberg [Tuesday, Nov 2, 2021 15:08]

another attempt :

(= 2+13 )


ser-castling in how many moves? Anticirce

- If the rook moved last, 1. Rxc1[Ra1] 2.000
- If the king moved last, 1. Kd1 2. Kxc1[Ke1] 3.000
- If last move not known, 1. Ra4 2. Rxe4[Rh1] 3. Kxe2[Ke1] 4.00
 
   
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(24) Posted by James Malcom [Tuesday, Nov 2, 2021 17:18]

Castling is illegal due to the black knight on e2 in the first two cases.
 
   
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(25) Posted by ichai [Tuesday, Nov 2, 2021 18:31]

Anticirce: b8 is occupied, the black knight cannot capture on black squares
 
 
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(26) Posted by Nikola Predrag [Tuesday, Nov 2, 2021 18:38]

Of course it's legal and in 3rd case, 3. Kxe2[Ke1] only regains wK's castling right.
 
   
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(27) Posted by James Malcom [Tuesday, Nov 2, 2021 21:39]

Ah, I see now; thanks. Anticirce and fairies in general can be muddling.
 
 
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(28) Posted by Andrew Buchanan [Wednesday, Nov 3, 2021 17:20]

Brave stuff extrapolating sensibly beyond the normal coverage of PRA.

One minor cavil: I don't think that we should talk about "with PRA" vs "without PRA". What varies is whether we are optimistic or pessimistic about whether each piece has moved. In either case, under PRA (the default protocol these days) we then fragment the problem into twins, being as optimistic & pessimistic as guided, and while avoiding illegal combinations.
 
   
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(29) Posted by Jacques Rotenberg [Wednesday, Nov 3, 2021 20:42]

Here is a way to show the idea, close to what I am looking for.
(No need to recall PRA) :

(= 2+13 )

Anticirce
ser-castling : how many moves?

- 1.00 ? illegal due to retro analysis
- If only the king moved before, 1.Kxe2[Ke1] 2.00
- If only the rook moved before, 1.Rh2 2.Rxe2[Rh1] 3.00 (1.Rxh3[Rh1}+?; 1.Rf1? 2.Rxf3[Rh1] 3.00??)
- If rook and king moved before, 1.Kf2 2.Rxc1[Ra1] 3.Kxf3[Ke1] 4.000 (3.Kxe2[Ke1]? 4.000??)
 
   
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(30) Posted by Andrew Buchanan [Thursday, Nov 4, 2021 02:00]

Thanks Jacques. I particularly liked the exact arrangement of bPs on the Queenside.
 
 
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(31) Posted by shankar ram [Thursday, Nov 4, 2021 15:18]

An interesting way to avoid PRA by varying the move lengths of each case and by "rebirthing" either the K, the R, or both.
Reminds me of a direct mate twin where the move length gets longer as the number of white pieces on the board are progressively reduced.
 
 
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MatPlus.Net Forum Retro/Math Castling