@inbookHilgert_1990, place=Berlin, title=Applications of Lie Semigroups in Analysis, booktitle=The Analytical and Topological Theory of Semigroups, publisher=De Gruyter, author=Hilgert, Joachim, editor=Hofmann, K.H. and et al., year=1990 
LibreCat: /record/51484

@articleHilgert_Hofmann_1990, title=On the Causal Structure of Homogeneous Manifolds, volume=67, journal=Math. Scand., author=Hilgert, Joachim and Hofmann, K.H., year=1990, pages=119–144 
LibreCat: /record/51446