Links
[1] https://www.ctsnet.org/user/login?destination=user/535689
[2] https://www.ctsnet.org/print/home/assen-keltchev
[3] https://www.ctsnet.org/article/endoscopic-avr-and-lima-lad-bilateral-minithoracotomy
[4] https://www.ctsnet.org/articles/Assen%20Keltchev
[5] https://www.ctsnet.org/society/ctsnet