the queen on b8
Deductive Puzzle #47
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is....?
Sep 16, 2009
0
#4
From the White pawn formation, the promoted pawn started out as the c-pawn. (The d-pawn is now on e3 after a dxe3 capture. The g-pawn is now on h3 after a gxh3 capture.) This also accounts for two captures of Black pieces, and only three Black pieces are missing. So, only one other capture is unaccounted for.
For the c-pawn to promote, the path it must have taken is forward to c6, then cxb7, then b8=Q, which accounts for the last capture. So, it seems likely the queen on b8 is the promoted pawn, although it's unclear to me how to prove the pawn couldn't have promoted on b8 and then ran around to g8.
We can see that it must be the c pawn that promoted and that there are three missing Black pieces. In order for the c-pawn to promote it would have had to have made at least one capture to get past the pawn still on c7 and since we can see that there were two other captures by pawns on e3 an h3 it's clear that it only captured once.
In order for it to have promoted, knowing that the Black Queen has not yet moved (and that d7 has been occupied only once) it's clear that the c-pawn promoted on b8 by first capturing a piece on b7.
That piece, and the piece captured on h3 must both have been rooks as they are both light squares and so can't have been where the dark-squared Black Bishop was captured. This means that the missing Black Bishop must have been captured on e3.
The capture on h3 had to have occurred before either of White's King-side Rook or light squared Bishop could have escaped so one of the Rooks must have been free before this happened. Additionally, the capture of the Bishop on e3 must have occurred before White's dark-squared bishop could have escaped. Since White is only missing three pieces, and the g6 square is light coloured, the capture on g6 must have been of either White's missing Rook or light-squared Bishop meaning that the capture on h3 that freed them must have in fact been Black's Queen-side Rook. in order for it to have been freed, the capture of White's dark squared Bishop must have occurred on b6 by Black's a-pawn, which of course means that the capture of Black's dark-squared Bishop occurred before that on e3.
So we now have all of the captures accounted for, and a rough sequence:
- Black plays d7-d5
- Black plays e5-e6 to allow the dark squared Bishop out
- Black's dark squared Bishop on e3
- White's dark squared Bishop on b6
- Black's Queen-side Rook on h3
- White's King-side Rook or light squared Bishop on g6 -- not sure which piece.
- Black's King-side rook to a8
- White's King-side Rook or light squared Bishop on a6 -- whichever wasn't captured on g6
- Black's King-side rook to b7
- Black's rook on b7 by White's c-pawn
- White's c-pawn promotes on b8
Finally, in order for the Queen currently not on b8 to be the promoted Queen, it would have had to have escaped and been replaced by the real queen. Knowing that the pawn structure was fixed in it's current state at the time of promotion the only way in or out is via c6 putting the King in check. Since we know the King hasn't moved the check must have been blocked by a piece on d7 -- but since we know that square was occupied only once (before the first move by Black's d-pawn) there's no way this can have happened so the Queen on b8 must be the promoted one.
Incidentally, the knowledge that White can still castle is presumably to indicate that the Rook didn't escape past the King, but instead must have done so on the g-file, but the key is in finding out that the h3 capture occurred first, and since it's required for the Bishop to escape, and the Bishop's escape is required for the rook to get out by moving through e1 that piece of information seems to be extraneous.
This one was tough -- I liked it.
Sep 16, 2009
0
#7
Grobe: After promoting, can't the pawn (now a queen) get to g8 by the route b7-a6-c4-etc., bypassing c6? Of course, this means ...a6 isn't played until after the promoted pawn has escaped.
No, because we know it was the Rook that was captured on b7, and in order for the rook to have gotten there the pawn on b7 would have already been on a6 to clear the road for it. This means that that route was closed off before the promotion.
Sorry Grobe, but there are some errors that I see there.
Yes -- I see them too now.
No, I take that back -- it looks sound to me.
Wait, shit. You're right. I'm just dyslexic apparently.
I usually start typing long before I actually have the puzzle solved on these, so the solution I provide is pretty much me working through my thought process on the problem from beginning to end. It's entirely possible that what I'm trying to get across is far from clear as a result....
Did I mention that I can't get enough of these?
My apologies for such a nasty little puzzle just earlier, here is a (slightly) more conventional one.
Which Queen is the original and which is promoted?
The following facts are known:
Black started the game with the d7 pawn moving to d5.
Black Royalty has not yet moved
White can still Castle
d7 has been occupied only once.