Computing epsilon-Free NFA from Regular Expressions in O(n log²(n)) Time. - Christian Hagenah; Anca Muscholl (MFCS, 1998)

Computing epsilon-free NFA from regular expressions in O(n log2(n)) time. - Christian Hagenah; Anca Muscholl (RAIRO Theor. Informatics Appl., 2000)

Gleichungen mit regulären Randbedingungen über freien Gruppen. - Christian Hagenah (2000)

The existential theory of equations with rational constraints in free groups is PSPACE-complete. - Volker Diekert; Claudio Gutierrez 001; Christian Hagenah (Inf. Comput., 2005)