When I in 1977 as a 13-years old boy first visited Kongsvinger Sjakklubb, one of the first sights that met me, was a group of adult players discussing whether it really was possible that this position could occur after only 4 moves:
I happily joined in with my suggestions but after 30 minutes of heavy thinking and discussion and a lot of aimless moving around, we concluded that it was impossible: The two knights simply could not both capture each other and it was not time for other pieces to capture them and return to its original squares.
Well, it turned out that it was possible after all, but only after the person who had offered the puzzle (standing sniggering in the background all the time) demonstrated the solution. Since that day I have had a fascination for this kind of retrograde puzzles, and collected whatever I have come across. Unfortunately the composer (originator/creator?) of the puzzle very rarely is provided.
Sometime around 2000, I was offered this seemingly related puzzle:
Can this position occur after only 5 moves? Surprisingly knowing the solution to the previous puzzle does not make it easier at all.
Judging from the reactions to puzzle No 7 at the
ChessBase Christmas Quiz, I am not the only chess-player fascinated by this kind of useless brain exercizes. You can safely look at the readers' feedback - all spoilers have been removed.
I will return with solutions (also for the ChessBase nut, which is quite hard) in a few days.
It seems that I cannot add a link to the ChessBase Christmas Quiz. I have no idea why, but here it is as a text string: http://www.chessbase.com/puzzle/christmas2006/chr06-9a.htm.
If you want to solve the puzzles yourself, be careful. I will allow spoilers in the Comments below (they will become visible if you open a post by clicking the header or if you click the "Comments" link below).