NguenTkhe Khoan, and FamNgok Boi. 1999. “On Continuous Dependence of Solutions of Linear Differential Equations on a Parameter in a Banach Space”. Ukrains’kyi Matematychnyi Zhurnal 51 (2), 275–280. https://umj.imath.kiev.ua/index.php/umj/article/view/4610.