One move Retrograde


One move Retrograde

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Paul Valle    (2011-01-19 02:07:18)
One move Retrograde

The following ChessPosition (see diagram) can be constructed from a normal game.

What was the last move made?

The answer has to be very specific:
-Witch side moved
-What piece is moved
-What square it moved from
-What square it arrives on
-and if a piece is taken, then you have to name that piece as well

Love this one! I was not able to crack this problem my self when I first tried. Wonder if anyone here will ...

a b c d e f g h

Josef Riha    (2011-01-19 09:25:08)
One move Retrograde

Hmm... there is no free square for the white knight to move from. So I think black did his last move: g6!
Or is this too simple?

Thibault de Vassal    (2011-01-19 12:51:05)
One move Retrograde

Well, in seconds my first impression was that White moved g7xf8N, the piece taken was Queen (by elimination of all other possibilities, which was stupid at the end as Queen was not possible either).

So Kg8xh8 looked more promising, taking Black Queen.

The piece taken cannot be rook (white to play & check)
The piece taken cannot be bishop (other black & all pawns remain)
The piece taken cannot be knight (previous move impossible)

In example: Black King is in h8, Qa2a1+, Kh8g8, Qh8+ Kxh8

...but there may be a trap?

Thibault de Vassal    (2011-01-19 13:00:16)
One move Retrograde

g6, Ng6f8, Kf8e8, Kg6f4, Re8e7 then Bh4d8... (in reverse order of course) looks possible as well finally. One of us is wrong, but why??

Thibault de Vassal    (2011-01-19 13:18:42)
One move Retrograde

Strange, the White King seems to be able to reach h8 in both cases, and the Black Queen seems to be able to leave d8..... I cannot find the reason but if there's only one solution, it is g6! cause the Black Queen on the board means a 'condition more' in the same situation while the idea with g6 is the same to put the White Knight in f8. So "by elimination" the answer is g6, but I guess that there is a better explanation, right? :)

Thibault de Vassal    (2011-01-19 13:42:52)
One move Retrograde

Okay, I was wrong (and my previous reasoning was completely wrong), the answer is Kg8xh8 (the queen) for the reasons I mentioned and g6 is not possible cause the White King cannot reach h8 with the Black Pawn in g7.

Paul Valle    (2011-01-19 15:08:34)
One move Retrograde

That's right Thibault!
1.Kg8xQh8 is the correct move for all the reasons you've mentioned.
Well done!