Asrorov, F. A., & Perestyuk, N. A. (1994). Green-Samoilenko function and existence of integral sets of linear extensions of nonautonomous equations. Ukrains’kyi Matematychnyi Zhurnal, 46(8), 1067–1071. https://umj.imath.kiev.ua/index.php/umj/article/view/5659