﻿ A Retro Problem by Stanislav Vokal

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Viktor Shishkin    (2011-09-20 21:04:22)
A Retro Problem by Stanislav Vokal

ChessPosition (see diagram) Position after 13. O-O-O. May Black castle?

 8 7 6 5 4 3 2 1
 a b c d e f g h

Thibault de Vassal    (2011-09-22 09:42:59)
A Retro Problem by Stanislav Vokal

Much more interesting than it seems at a first sight :)

Philip Roe    (2011-09-22 15:13:14)
A Retro Problem by Stanislav Vokal

The answer is no. Black must have moved either his K or his KR. The demonstration makes use of the fact that Knights cannot gain or lose a single move.

White has played the following eleven moves or their equivalents. Ng1-f3-h4-g6xBf8-g6, Nb1-c3-b5, axb3, f3, h3, Rg1 plus other move that must have been Qc1. Black has played the following nine moves or their equivalents. Nb8-c6-d4-b3xBc1-b3xQc1-b3, Nh6, hxg6. He has three moves left.

If any piece has moved twice, there is no possibility for the one remaining move. Therefore he must have made these three moves with either K or KR.

Dariusz Fraczek    (2011-11-22 18:21:01)
A Retro Problem by Stanislav Vokal

I think that we cannot say. Depending on previous black moves black may:
- castle both kingside and queenside,
- castle only kingside,
- castle only queenside,
- castle is not possible.
For example: 1. Na3 Nc6 2. Nb5 Nd4 3. Nf3 Nb3 4. Ne5 Nxc1 5. Ng6 Nb3 6. Qc1 Nxc1 7. Nxf8 Nb3 8. axb3 Nh6 9. Ng6 hxg6 10. f3 f6 11. h3 - and now:
- 11... Ng8 12. Rg1 Nh6 13. O-O-O,
- 11... Rb8 12. Rg1 Ra8 13. O-O-O,
- 11... Rg8 12. Rg1 Rh8 13. O-O-O,
- 11... Kf8 12. Rg1 Ke8 13. O-O-O.

Philip Roe    (2011-12-13 22:30:08)
A Retro Problem by Stanislav Vokal

Dariusz, You seem to be right. I had overlooked that Black had also played f6 in addition to the moves I gave, and therefore only needs to make two "spare" moves, which is easy.

Victor, can you explain?

 January 24, 2020

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