Coreference

1968	1970	1981	1990	2000	2010
	1973	1983	1991	2001
	1974	1984	1992	2002
	1976	1985	1993	2003
	1977	1986	1994	2004
	1978	1987	1995	2005
	1979	1988	1996	2006
		1989	1997	2007
			1998	2008
			1999	2009