3 http://hdl.handle.net/10338.dmlcz/116883 3 Seventieth anniversary of birthday of Academician Štefan Schwarz http://hdl.handle.net/10338.dmlcz/101974 Seventieth anniversary of birthday of Academician Štefan Schwarz 85 years of Academician Otakar Borůvka http://hdl.handle.net/10338.dmlcz/101973 85 years of Academician Otakar Borůvka Modular groupoids http://hdl.handle.net/10338.dmlcz/101972 Modular groupoids A directed $d$-group that is not a group of divisibility http://hdl.handle.net/10338.dmlcz/101971 A directed $d$-group that is not a group of divisibility