Root lattice and features of empty-root system in indefinite Kac-Moody ID_n(a)
ZHAO Chun-yuan1;HU Yu-hong2;ZHANG Li-li3(1.Shenyang Electric Power Institute;Shenyang 110036;China;2.Liaoning Electric Power Profession Institute;Shenyang 110016;China;3.Beijing Education and Science Research Institute;Beijing 100031