ZHELIAZKOV, G.; IVANOVA, D.; GEORGIEV, I. On the planning of the socio-economic development of the Municipality of Tvarditsa (Bulgaria). Responsibility and Sustainability, [S. l.], v. 1, n. 2, p. 69–74, 2013. Disponível em: https://responsibility-sustainability.org/index.php/R-S/article/view/16. Acesso em: 27 apr. 2025.