1. BESSENRODT, C., H. H. BRUNGS, G. TÖRNER, Chain Rings, Part IIa, Schriftenreihe der Universität Duisburg, Nr. 52 Preprint (1986).
2. BOTTO-MURA, R. T., H. H. BRUNGS, J. FISHER, Chain Rings and Valuation Semigroups, Comm. Algebra5 (1977) 14, 1529–1547.
3. BROWN, K., Cohomology of Groups, Berlin, Heidelberg, New York, Springer 1982.
4. BRUNGS, H. H., G. TÖRNER, Right Invariant Right Holoids, submitted for publication in Comm. Algebra.
5. CLIFFORD, A. H., Naturally Totally Ordered Commutative Semigroups, Amer. Jour. Math.76 (1954), 631–646.