Vasile Dragan, Ivan G. Ivanov, Viorica Dragan, Date of publication: March 1,2018 PDF
Konstantin Kolev, Maya Tsoklinova, Date of publication: September 1,2018 PDF
Vasile Dragan, Hiroaki Mukaidani, Ivan G. Ivanov, Date of publication: September 15,2018 PDF
Maya Tsoklinova, Konstantin Kolev, Date of publication: October 30,2018 PDF
Borislava Brigazova, Date of publication: December 20,2018 PDF