LI , WEI-NIAN, and BAO-TONG CUI. “OSCILLATION OF SOLUTIONS OF PARABOLIC EQUATIONS OF NEUTRAL TYPE”. Tamkang Journal of Mathematics 30, no. 4 (December 1, 1999): 331–338. Accessed May 6, 2024. https://journals.math.tku.edu.tw/index.php/TKJM/article/view/4239.