Perfect elements in the free modular lattices
In: Mathematische Annalen, Jg. 247 H. 2, S. 95-100
The preprojective algebra of a modulated graph
In: Representation Theory II. Proceedings of the Second International Conference on Representations of Algebras, Ottawa, Carleton University, August 13-25, 1979: No. 2, Jg. 832, S. 216-231