Chessville - Chessprints - For the sheer JOY of chess! - Chess Positions from chess games, chess compositions, chess studies, etc.

Chessville
...by Chessplayers, for Chessplayers!

Today is

Site Map

If you have disabled Java for your browser, use the Site Map (linked in the header and footer).

Chessville
logo by
ChessPrints

Advertise
with
Chessville!!

Advertise to
thousands
of chess
fans for
as little
as $25.

Single insert:
$35
x4 insert:
@ $25 each.

From the
Chessville
Chess Store

Chessprint
August 26, 2007

Which white bishop is the original? - Solution

[Index of Chessprints]

Chess Books & Supplies

Convekta

Software & Databases You Can Actually Use!

NM Todd Bardwick

These stores
are now
open for business
here at the
Chessville Mall

Special
of the Month

Check back tomorrow!

Chessville
thanks you
for your
support!

Chess Posters

Online Chess Servers

Great places to play chess on the internet, not to mention all of the other services they provide, including lectures, banter games, tournaments, ratings, and so on.

Coming Soon!

Solution

Today we bring you another example of Retrograde Analysis, and this one comes from Raymond Smullyan, author of, among other books, Chess Mysteries of the Arabian Knights, from which this position is taken.
The story Prof. Smullyan writes to accompany the diagram, we omit. The basic problem here is to figure out which of the two light-squared white bishops was promoted, and which was the original.

The solution, each step feeding off the one before, goes something like this:

The only missing white pawn is the g-pawn, and it had to be the pawn that promoted because otherwise the promoted pawn would have to be the e-pawn (the only other pawn which might have promoted.) However that means the e-pawn would have had to capture twice (e-f-g) and likewise the g-pawn would have had to capture twice (g2xf3xe4.) That adds up to four captures, but Black is only missing three pieces, so the original e-pawn can not have been the pawn that promoted.
The black pawn on f6 had to have captured on that square before the white pawn promoted, else the white pawn would have had to capture twice to get around it (g-h-g). One of the captured black pieces would have been the h8-rook, but the other two missing black pieces are the a8-rook (which had to have been captured on a7, a8, or b8) and the dark-squared bishop, which cannot have left it's home at f8 before the g7-pawn moved. Hence, Black played g7xf6 before the white pawn promoted.
The piece Black captured on f6 had to be White's dark-squared bishop, White's only missing piece. In order to get to f6, the white bishop had to first get off c1, hence White's pawn move b3 occurred before the capture ...g7xf6. That means it also occurred before the white pawn promoted.
Since the bishop on a2 could never have gotten there after White played b3, it had to get there before, which means it also got there before the pawn promotion occurred. Hence, the bishop on g2 has to be the promoted one.