l1/2005-1/2004l+l1/2004-1/2003l-l1/2005-1/2003l
=(1/2004-1/2005)+(1/2003-1/2004)-(1/2003-1/2005)
=1/2004-1/2005+1/2003-1/2004-1/2003+1/2005
=0