VAITKUS, E. At the Discussion Club. Problemos, [S. l.], v. 1, p. 136–139, 1968. DOI: 10.15388/Problemos.1968.1.5718. Disponível em: https://test.zurnalai.vu.lt/problemos/article/view/5718. Acesso em: 27 oct. 2025.