Bleistein, Norman, and Richard A. Handelsman. Asymptotic Expansions of Integrals. New York: Dover Publications, 1986. Print.
de Bruijn, M. G. Asymptotic Methods in Analysis. 3rd ed. New York: Dover, 1981. Print.
Simmonds, James G., and James E. Mann. A First Look at Perturbation Theory. 2nd ed. Mineola, N.Y.: Dover Publications, 1998. Print.
Tricomi, F G. Integral Equations. Dover Publications, 2012. Print.