Dumanyan, V.Zh. “ON THE BOUNDEDNESS OF A CLASS OF THE FIRST ORDER LINEAR DIFFERENTIAL OPERATORS”. Proceedings of the YSU A: Physical and Mathematical Sciences 45, no. 1 (224) (February 16, 2011): 3–6. Accessed July 3, 2024. https://journals.ysu.am/index.php/proceedings-phys-math/article/view/vol45_no1_2011_pp003-006.