G. Marinov, V. Alexiev, and Y. Djonev. Artifical Intelligence: Methodology, Systems, and Applications (AIMSA'94), page 109-118. Sofia, Bulgaria, World Scientific Publishing, (September 1994)
V. Alexiev, P. Tarkalanov, N. Georgiev, and L. Pavlova. Digital Presentation and Preservation of Cultural and Scientific Heritage (DIPP 2020), 10, Burgas, Bulgaria, Institute of Mathematics and Informatics (IMI BAS), Sofia, (September 2020)