DRYGAŁA, D. POWER SET-problems with understanding the idea. Annales Universitatis Paedagogicae Cracoviensis Studia Mathematica, [S. l.], v. 3, p. 39–44, 2003. Disponível em: https://studmath.uken.krakow.pl/article/view/13464. Acesso em: 30 oct. 2026.