CIPLEA, Sorina Anamaria, and Nicolaie LUNGU. “Ulam Stability of Volterra Integral Equation on a Generalized Metric Space”. Studia Universitatis Babeș-Bolyai Mathematica, vol. 65, no. 2, June 2020, pp. 303–308, doi:10.24193/subbmath.2020.2.11.