SkrypnikW. I. “Kirkwood–Salsburg Equation for a Quantum Lattice System of Oscillators With Many-Particle Interaction Potentials”. Ukrains’kyi Matematychnyi Zhurnal, Vol. 61, no. 5, May 2009, pp. 689-00, https://umj.imath.kiev.ua/index.php/umj/article/view/3051.