Barbulyak, V. S., and Yu. G. Kondratiev. “Periodic Gibbs States”. Ukrains’kyi Matematychnyi Zhurnal 45, no. 4 (April 25, 1993): 451–458. Accessed April 14, 2025. https://umj.imath.kiev.ua/index.php/umj/article/view/5831.