SIMON, László. “On a System of Nonlinear Partial Functional Differential Equations of Different Types”. Studia Universitatis Babeș-Bolyai Mathematica, vol. 61, no. 2, June 2016, pp. 177-94, https://studia.reviste.ubbcluj.ro/index.php/subbmathematica/article/view/5551.