Teymurazyan, R. R. “TWO SIDE ESTIMATES FOR THE DOUBLE OBSTACLE PROBLEM”. Proceedings of the YSU A: Physical and Mathematical Sciences 43, no. 1 (218) (February 19, 2009): 8–15. Accessed July 22, 2024. https://journals.ysu.am/index.php/proceedings-phys-math/article/view/vol43_no1_2009_pp008-015.