LaraT., MatkowskiJ., MerentesN., QuinteroR., and WróbelM. “A Generalization of M-Convexity and a Sandwich Theorem”. Annales Mathematicae Silesianae, Vol. 31, Apr. 2017, pp. 107-26, https://www.journals.us.edu.pl/index.php/AMSIL/article/view/13943.