Dourmishev, Lyubomir A.
Guleva, Dimitrina V.
Miteva, Ljubka G.
Article History
Received: 19 June 2017
Accepted: 4 August 2017
First Online: 1 September 2017
Conflict of interest
: L.A. Dourmishev, D.V. Guleva, and L.G. Miteva declare that they have no competing interests.