MACH, A.; MOSZNER, Z. Unstable (Stable) system of stable (unstable) functional equations. Annales Universitatis Paedagogicae Cracoviensis Studia Mathematica, [S. l.], v. 9, p. 43–48, 2010. Disponível em: https://studmath.uken.krakow.pl/article/view/13244. Acesso em: 30 oct. 2026.