全苏数学奥林匹克：变换
	文章来源: 于德利 于 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.