Analysis of information sources in references of the Wikipedia article "%D0%91%D0%B8%D1%82%D0%BA%D0%B8 %D0%BD%D0%B0 %D0%9E%D1%81%D0%BC%D0%B0%D0%BD%D1%81%D0%BA%D0%B0%D1%82%D0%B0 %D0%B8%D0%BC%D0%BF%D0%B5%D1%80%D0%B8%D1%8F" in Bulgarian language version.
