1. C. V. Pao, Nonlinear Parabolic and Elliptic Equations (Plenum, New York, 1992).
2. A. B. Vasil’eva and V. F. Butuzov, Asymptotic Methods in the Theory of Singular Perturbations (Vysshaya Shkola, Moscow, 1990) [in Russian].
3. N. N. Nefedov, “Method of Differential Inequalities for Certain Singularly Perturbed Problems with Internal Layers,” Differ. Uravn. 31, 1132–1139 (1995).
4. 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)].
5. N. N. Nefedov and A. G. Nikitin, “Method of Differential Inequalities for Step-Like Contrast Structures in Singularly Perturbed Integro-Differential Equations in the Spatially Two-Dimensional Case,” Differ. Uravn. 42, 690–700 (2006) [Differ. Equations 42, 739–759 (2006)].