KATZOUNOV, V. Bulgaria’s Participation in the System of Joint Acquisition of Enemy Data (SOUD). Aparat Represji w Polsce Ludowej 1944-1989, [S. l.], n. 18, p. 447–456, 2023. DOI: 10.48261/ARPRL201816. Disponível em: https://czasopisma.ipn.gov.pl/index.php/arpl/article/view/1681. Acesso em: 8 lip. 2024.