M. F. Gorodnii, “On the invertibility of the operator d/dt + A in certain functional spaces”, Ukr. Mat. Zhurn., vol. 59, no. 8, pp. 1020–1025, Aug. 2007, Accessed: Dec. 06, 2025. [Online]. Available: https://umj.imath.kiev.ua/index.php/umj/article/view/3365