Oscillation of third order self-adjoint differential equations

In this paper, the general third order self-adjoint differential equations (A[raised +]) (r(x) [(r(x)y')' + q(x)y])' + q(x)r(x)y' = 0 and (A[raised -]) (r(x)[(r(x)y')' - q(x)y])' - q(x)r(x)y' = 0 are studied with respect to the general second order self-adjoint differential equations (B[raised +]) 2(r(x)y')' + q(x)y = 0 and (B[raised -]) 2(r(x)y')' - q(x)y = 0 on the half axis [a,[infinity]). The coefficient functions q(x) and r(x) are assumed to be positive real-valued continuous functions. Existence of oscillatory and nonoscillatory solutions of (A[raised +]) and (A[raised -]) is investigated, as well as boundedness and asymptotic behavior of such solutions. Separation and comparison theorems are established for (A[raised +]).