1975-present Sofia University, Sofia, Bulgaria.
1975-present Institute of Mathematics and Computer Science, Bulgarian Academy of Sciences, Sofia, Bulgaria.
1982-present IEI Pisa, Italy.
1991-present University of Amsterdam, Amsterdam, The Netherlands.
1991-present University of Toronto, Canada.
1996-present University of Lincoln and Humbersite, UK.
2000-present University of Calgary, Alberta, Canada.
2002- present Polytechnic School, University of Nantes, France