[1] Howes, F.A., Differenual inequalities and applications to nonlinear singular perturbation problems, J. of Diff. Eqs., 20(1976), 133-149.
[2] Chang, K.W. and F.A.Howes, Nonlinear Singular Perturbation Phenomena: Theory and Applications, Springer-Verlag. New York, Berlin, Heidelberg. Tokyo(1984).
[3] O'Malley, R.E., Introduction to Singular Perturbations, Academic Press(1974).
[4] Lin Zong-chi and Zheng Yong-shu, Singular perturbation of boundary problem of higherorder ordinary differential equations(I), Journal of Fujian Normal University,(Edition on Natural Science), 2(1980), 13-27.(in Chinese)
[5] Liu, G.X., About singularly perturbed quasilinear systems, Applied Mathematics and Mechanics, 8, 11(1987), 1027-1036.
[6] Kelley, W.G., A geometric method of studying two point boundary value problems for second order systems, Rocky Moun. J. of Math., 7(1977), 251-263.
[7] Kelley, W.G., Boundary value problems for pairs of second order equations containing a small parameter, Rocky Moun. J. Math., 12, 4(1982), 655-667.