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C00002 00002		SOME ISSUES IN ARTIFICIAL INTELLIGENCE SUGGESTED BY A CHESS PUZZLE
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	SOME ISSUES IN ARTIFICIAL INTELLIGENCE SUGGESTED BY A CHESS PUZZLE


	The following problem due to Raymond Smullyan appeared in
\F1Scientific American\F0 for April 1974: "The illustration above shows
the position of an end game with only five men on the board: the black
and white kings, two white pawns and one pawn of unknown color.  During
the game no piece has moved from a square of one color to a square of
another color.  Is the unknown pawn white or black?"  In the accompanying
diagram the white king is on his Q6, the black king is on his KB2, the
white pawns are on white's Q2 and KB2, and the unknown pawn is on white's
KN3.

	An informal statement of the solution is as follows: the white K
cannot have reached its position solely by non-castling moves, because the
two white pawns block it from doing so staying on black squares and they
can't ever have moved.  White cannot have castled on the Q side, because
that would change the color of the rook.  If the unknown pawn were white, it
would have had to have come from KR3 by a capture, but whether there or on
KN3, it would block the white king from getting out.  Therefore, the unknown
pawn must be black.  That it could be black can be proved by exhibiting
a game leading to the position.

	I apologize to the reader of this note for having deprived him of
the fun of solving the puzzle himself, but our business is elsewhere.