S. C. Tefteller, Oscillation of Second Order Nonhomogeneous Linear Differential Equations, SIAM Journal on Applied Mathematics, Vol. 31, No. 3 (Nov., 1976), pp. 461-467 ...

F. W. J. Olver, The Asymptotic Solution of Linear Differential Equations of the Second Order in a Domain Containing One Transition Point, Philosophical Transactions of the Royal Society of London.

Introduction to differential equations. Topics include methods of solutions for linear and non-linear first order differential equations, linear second order differential equations, higher order ...