Kozactvo v dokumentach tovarystv ukraïnsʹkoï diaspory v Bolhariï (1921-1939) = Kazačestvo v dokumentach obščestv ukrainskoj diaspory v Bolgarii : (1921-1939) = Cossacks in the documents of the companies Ukrainian diasporain Bulgaria : (1921-1939) - Bačynsʹka, Olena Anatoliïvna 1971-; Hromovyč, Uljana (2017)