1. N. Chuensupantharat, P. Kumam, S. Dhompongsa, A graphical proof of the Brouwer fixed point theorem. Thai J. Math. 15(3), 607–610 (2017)
2. S. Dhompongsa, J. Nantadilok, A simple proof of the Brouwer fixed point theorem. Thai J. Math. 13(3), 519–525 (2015)
3. S. Dhompongsa, P. Kumam, An elementary proof of the Brouwer fixed point theorem. Thai J. Math. 17(2), 539–542 (2019)
4. I. Ekeland, Sur les problèmes variationnels. C. R. Acad. Sci. Paris Sér. A-B 275, A1057–A1059 (1972)
5. M.A. Khamsi, Remarks on Caristi’s fixed point theorem. Nonlinear Anal. 71(1–2), 227–231 (2009)