Affiliations: Stanislav Sysala, Institute of Geonics of the Czech Academy of Sciences, Studentská 1768, 708 00 Ostrava, Czech Republic, e-mail: stanislav.sysala@ugn.cas.cz; Petr Tichý, Charles University, Faculty of Mathematics and Physics, Sokolovská 83, 186 75 Praha 8, Czech Republic, e-mail: ptichy@karlin.mff.cuni.cz