1. Aleksandrova N. Malka knizhka za golyamata samota [The small book about great loneliness]. Sofia, Bulgaria: Prof. Petko Venedikov, 2015. 129 p. (In Bulg.).
2. Andreichin L. Iz istoriyata na nasheto ezikovo stroitelstvo [From the history of our language construction]. Sofia, Bulgaria: Narodna prosveta, 1977. 255 p. (In Bulg.).
3. Vodopâyanova N.E. Psikhodiagnostika stressa [Psychodiagnostics of stress]. Saint Petersburg: Piter, 2009. 329 p.
4. Kryukova T.L., Ekimchik O.A., Opekina T.P. Psikhologiya sovladaniya s trudnostyami v blizkikh (mezhlichnostnykh) otnosheniyakh [Psychology of coping with difficulties in close (interpersonal) relationships]. Kostroma: KGU Publ., 2019. 340 p.
5. Osin E.N., Leontâev D.A. Differentsialânyi oprosnik perezhivaniya odinochestva: struktura i svoistva [Differential questionnaire of loneliness: Structure and characteristics]. Psikhologiya. Zhurnal Vysshei shkoly ekonomiki = Psychology. Journal of the High School of Economics, 2013. Vol. 10 (1), pp. 55â81.