Q. Chuanxi and G. Ladas: Linearized oscillations for equations with positive and negative coefficients
. Hiroshima Math. J. 20 (1990), 331–340. MR 1063367
 I. Györi and G. Ladas: Oscillation Theory of Delay Differential Equations with Applications
. Clarendon Press, Oxford, 1991. MR 1168471
 G. Ladas: Linearized Oscillation For Neutral Equations, Lecture Notes in Pure and Applied Mathematics, Differential Equations
. Marcel Dekker, Inc., New York, 1990, pp. 379–387. MR 1021738
 J. S. Yu and M. P. Chen: Linearized oscillation for first order neutral delay differential equations. Panamer. Math. J. 2 (1993).
 J. H. Shen, J. S. Yu and X. Z. Qian: A linearized oscillation result for odd-order neutral differential equations. J. Math. Anal. Appl. 185 (1994).