Regular Languages up to Star Height 1 and the Difference Shrinking Acceptance Probability. - Michael Hartwig; Somnuk Phon-Amnuaisuk (TMFCS, 2008)

On the Density of Regular and Context-Free Languages. - Michael Hartwig (Discret. Math. Algorithms Appl., 2010)

On the Relationship between Proof Writing and Programming: Some Conclusions for Teaching Future Software Developers. - Michael Hartwig (ICSECS (3), 2011)