Sharp oscillation theorem for fourth-order linear delay differential equations

In this paper, we present a single-condition sharp criterion for the oscillation of the fourth-order linear delay differential equation x(4)(t)+p(t)x(τ(t))=0\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$ x^{(4)}(t) + p(t)x\bigl(\tau (t)\bigr) = 0 $$\end{document} by employing a novel method of iteratively improved monotonicity properties of nonoscillatory solutions. The result obtained improves a large number of existing ones in the literature.