SOLOVJOVAS, Nikolajus. Neighbourhood Relations. Problemos, [S. l.], v. 15, p. 98–103, 1975. DOI: 10.15388/Problemos.1975.15.5578. Disponível em: https://test.zurnalai.vu.lt/problemos/article/view/5578. Acesso em: 25 oct. 2025.