Kozák, I., and Gy. Szeidl. “Complete Solution for Stresses in Terms of Stress Functions. Part I: Derivation from the Principle of Virtual Work”. Technische Mechanik - European Journal of Engineering Mechanics, vol. 16, no. 2, Oct. 2019, pp. 147-68, https://journals.ub.ovgu.de/index.php/techmech/article/view/1228.