Fx. Liang, THE DISTRIBUTION OF ZEROS OF SOLUTIONS OF FIRST-ORDER DELAY-DIFFERENTIAL EQUATIONS, Journal of mathematical analysis and applications, 186(2), 1994, pp. 383-392
We give two estimates of the distance between adjacent zeros of the so
lutions of the first-order delay differential equation x'(t) + p(t)x(t
- tau) = 0. (C) 1994 Academic Press, Inc.