Originally posted by tomtom232
that does not matter in a problem. it doesn't have to be a legal position.
If you don't have a legal position, it's not a
chess problem anymore. If the rules of the game don't matter, or can be violated at will, then why not move the King three squares at a time to get out of checkmate?
This is exactly why chess problem magazines will not accept originals with illegal positions (the exception is chess variant problems).
Edit: Here are two links illustrating the convention of legality.
http://www.math.harvard.edu/~elkies/FS23j.03/glossary_chess.html
"Legal position (n.): a position that can be reached from the initial array by game consisting entirely of legal moves, however bizarre.
Conventionally any chess problem should have a legal position." (emphasis mine)
http://www.bcps.knightsfield.co.uk/introduction.html
"Position
Chess problems do not use positions taken from games. A diagram inviting you to work out how a chess player overcame his opponent is hopefully interesting, intriguing and instructive, but it is not a chess problem. The position of a chess problem is created by a Composer (or Problemist).
By convention the position should be legal, that is, it must be capable of arising in a game of chess, however unlikely the moves leading up to it may have been." (emphasis mine)
Edit 2: And finally, the killer, from the FIDE Codex of Chess Composition: (http://www.sci.fi/~stniekat/pccc/codex.htm)
"Chapter IV - Miscellaneous Conventions
Article 14 - Legality of Positions
(1) A position is legal if it can be reached by a sequence of moves from the initial array [17]. Otherwise, the position is called illegal [18].
(2) In studies and problems that apply the FIDE-rules,
illegal positions are not acceptable for composition tournaments unless the tournament conditions so stipulate." (emphasis mine)