1. C. V. Pao, Nonlinear Parabolic and Elliptic Equations (Plenum, New York-London, 1992).
2. N. N. Nefedov and A. G. Nikitin, “The Asymptotic Method of Differential Inequalities for Singularly Perturbed Integro-Differential Equations,” Differ. Uravn. 36, 1398–1404 (2000) [Differ. Equations 36, 1544–1550 (2000)].
3. N. N. Nefedov and A. G. Nikitin, “Development of the Asymptotic Method of Differential Inequalities for Step-Type Solutions of Singularly Perturbed Integro-Differential Equations,” Zh. Vychisl. Mat. Mat. Fiz. 41, 1057–1066 (2001) [Comput. Math. Math. Phys. 41, 1005–1014 (2001)].
4. V. F. Butuzov, N. N. Nefedov, and K. R. Schneider, “Singularly Perturbed Problems in Case of Exchange of Stabilities,” J. Math. Sci. 121, 1973–2079 (2004).
5. N. N. Nefedov, “Method of Differential Inequalities for Some Singularly Perturbed Problems with Internal Layers,” Differ. Uravn. 31, 1132–1139 (1995).