Mathematica Slovaca. Bratislava : Slovenská akadémia vied, Matematický ústav SAV, 2020. Available on Internet: <https://www.degruyter.com/view/journals/ms/70/6/ms.70.issue-6.xml> <https://www.sav.sk/?lang=sk&doc=journal-list&journal_no=17> ISSN 0139-9918.