Gorodnii, M. F. “On the Invertibility of the Operator <i>d</i>/<i>dt </i> + <i>A</I&gt; in Certain Functional Spaces”. Ukrains’kyi Matematychnyi Zhurnal 59, no. 8 (August 25, 2007): 1020–1025. Accessed May 5, 2024. https://umj.imath.kiev.ua/index.php/umj/article/view/3365.