1. Lepin, L.A., Generalized Solutions and the Solvability of Boundary Value Problems for a Second-Order Differential Equation, Differ. Uravn., 1982, vol. 18, no. 8, pp. 1323–1330.
2. Lepin, A.Ya. and Lepin, L.A., Kraevye zadachi dlya obyknovennogo differentsial’nogo uravneniya vtorogo poryadka (Boundary Value Problems for a Second-Order Ordinary Differential Equation), Riga: Zinatne, 1988.
3. Crandall, M.G. and Lions, P.-L., Viscosity Solutions of Hamilton-Jacobi Equations, Trans. Amer. Math. Soc., 1983, vol. 277, no. 1, pp. 1–42.
4. De Coster, C., Pairs of Positive Solutions for the One-Dimensional φ-Laplacian, Nonlinear Anal., 1994, vol. 23, no. 5, pp. 669–681.
5. Cabada, A. and Pouso, R.L., Existence Result for the Problem (g4(u′))′ = f(t, u, u′) with Periodic and Neumann Boundary Conditions, Nonlinear Anal., 1997, vol. 30, no. 3, pp. 1733–1742.