1. Technical University of Gdańsk, Department of Applied Informatics, Technical University of Gdańsk, Ul. G. Narutowicza 11/12, PL80-952 Gdańsk, Poland.
2. Bulgarian Academy of Sciences, Linguistic Modelling Laboratory, LPDP—Bulgarian Academy of Sciences, Bulgaria.
3. University of Pretoria, Department of Computer Science, University of Pretoria, Pretoria 0002, South Africa.
4. E-mail: