Hilgert, Joachim. “Applications of Lie Semigroups in Analysis.” The Analytical and Topological Theory of Semigroups, edited by K.H. Hofmann and et al., De Gruyter, 1990.
LibreCat: /record/51484

Hilgert, Joachim, and K. H. Hofmann. “On the Causal Structure of Homogeneous Manifolds.” Math. Scand., vol. 67, 1990, pp. 119–44.
LibreCat: /record/51446