Oscillation of arbitrary-order derivatives of solutions to the higher order non-homogeneous linear differential equations taking small functions in the unit disc

In this article, we study the relationship between solutions and their arbitrary-order derivatives of the higher order non-homogeneous linear differential equation f((k)) + A(k-1)(z)f((k-1)) + . . . + A(1)(z)f' + A(0)(z)f = F(z) in the unit disc Delta with analytic or meromorphic coefficients of finite [p, q]-order. We obtain some oscillation theorems for f((j))(z) - phi(z), where f is a solution and phi(z) is a small function.