PORWAL, Saurabh, et al. “Some New Subclasses of Bi-Univalent Functions”. Studia Universitatis Babeș-Bolyai Mathematica, vol. 60, no. 4, Dec. 2015, pp. 543-52, https://studia.reviste.ubbcluj.ro/index.php/subbmathematica/article/view/5830.