NEČAS, J. The memory of Jan Heller. Envigogika, Praha, Czech Republic, v. 3, n. 1, 2008. DOI: 10.14712/18023061.133. Disponível em: https://envigogika.czp.cuni.cz/index.php/Envigogika/article/view/133. Acesso em: 5 dec. 2020.