On the Borel Inseparability of Game Tree Languages. - Szczepan Hummel; Henryk Michalewski; Damian Niwinski (STACS, 2009)

On the Topological Complexity of MSO+U and Related Automata Models. - Szczepan Hummel; Michal Skrzypczak; Szymon Torunczyk (MFCS, 2010)

Unambiguous Tree Languages Are Topologically Harder Than Deterministic Ones - Szczepan Hummel (GandALF, 2012)

The Topological Complexity of MSO+U and Related Automata Models. - Szczepan Hummel; Michal Skrzypczak (Fundam. Informaticae, 2012)

On Unambiguous Regular Tree Languages of Index (0, 2). - Jacques Duparc; Kevin Fournier; Szczepan Hummel (CSL, 2015)