We consider the symmetry of lattice su(n) spin systems with inverse sq
uare exchange; the Haldane-Shastry model and the Polychronakos-Frahm m
odel, It is shown that both systems have yangian symmetry for a finite
number of sites, Based on the yangian symmetry the energy spectrum is
considered. Furthermore the representation for motifs and the relatio
ns with the Virasoro character for su(n) level-1 Wess-Zumino-Witten th
eory are discussed.