Comparison Theorem for Conjugate Points of a Fourth-order Linear Differential Equation

In 1961, J. Barrett showed that if the first conjugate point eta(1) (a) exists for the differential equation (r(x)y '')'' = p(x)y, where r(x) > 0 and p(x) > 0, then so does the first systems-conjugate point (eta) over cap (1)(a). The aim of this note is to extend this result to the general equation with middle term (q(x)y')' without further restriction on q(x), other than continuity.