1. Riga State Gymnasium No. 1, 8 Raina Boulevard, Riga LV-1050, Latvia
2. Faculty of Humanities, Leiden University Rapenburg 70, 2311 EZ Leiden, the Netherlands
3. Department of Aviation Transport, Transport and Telecommunication Institute, 1 Lomonosov Street, Riga LV-1019, Latvia
4. Institute of Mathematical Sciences and Information Technologies, Liepaja University, 14 Liela Street, Liepaja LV-3401, Latvia