1. Boucenna, A., Briki, M., Moussaoui, T., O’Regan, D.: Minimization principle in ordered Banach spaces and application via Ekeland’s variational principle. Differ. Equ. Appl. 9(1), 99–104 (2017)
2. Brezis, H.: Functional Analysis. Sobolev Spaces and Partial Differential Equations. Springer, Berlin (2011)
3. Briki, M., Djebali, S., Moussaoui, T.: Solvability of an impulsive boundary value problem on the half-line via critical point theory. Bull. Iran. Math. Soc. 43(3), 601–615 (2017)
4. De Figueiredo, D.G.: Lectures on the Ekeland Variational Principle with Applications and Detours, TATA Institute. Springer, Berlin (1989)
5. Delbaen, F., Schachermayer, W.: A general version of the fundamental theorem of asset pricing. Math. Ann. 300(3), 463–520 (1994)