NATH, P.; SINGH, D. K. On a sum form functional equation containing three unknown mappings. Annales Universitatis Paedagogicae Cracoviensis Studia Mathematica, [S. l.], v. 12, p. 69–81, 2013. Disponível em: https://studmath.uken.krakow.pl/article/view/13185. Acesso em: 31 oct. 2026.