1
Published 2006
University of National and World Economy

2
Published 2006
Rectors Conference of the Republic of Bulgaria

3
Published 2011
WWF Danube-Carpathian Programme

4
Published 2007
Mid Yorkshire Chamber of Commerce and Industry - Branch Bulgaria

5
Published 2008
Rectors Conference of the Republic of Bulgaria

6
by Gesemann, Wolfgang
Published 1982
Hieronymus-Verl.

7
by Comati, Sigrun
Published 1988
Sagner

8
Published 2017
OECD Publishing