全蘇數學奧林匹克：變換
	文章來源: 於德利 於 2007-12-28 17:41:55

A move replaces the real numbers a, b, c, d by a-b, b-c, c-d, d-a. If a, b, c, d are not all equal, show that at least one of the numbers can exceed 1985 after a finite number of moves.