1. Advanced Mathematical Methods for Scientists and Engineers;Bender,1978
2. Functions of a Complex Variable;Carrier,1966
3. “Sufficient Conditions for the Uniform Convergence of a Difference Scheme for a Singularly Perturbed Turning Point Problem,”;Farrell;SIAM J. Numer. Anal.,1988
4. “The WKB-Method for a Non-Linear Equation of the Second Order,”;Fedoryuk;U.S.S.R. Comput. Maths. Math. Phys.,1986
5. “Generalised WKBJ Formulae,”;Giler;J. Phys. A: Math. Gen.,1988