1. G. C. L. Br�mmer, E. Giuli, and H. Herrlich: Epireflections which are completions,Cahiers Topologie G�om. Diff�rentielle Cat�goriques 33 (1992), 71?93.
2. D. Dikranjan and E. Giuli: Closure operators I,Topology Appl. 27 (1987), 129?143.
3. D. Dikranjan and E. Giuli: Preradicals, factorizations and compactness in categories of modules, preprint, L'Aquila, 1990.
4. D. Dikranjan, E. Giuli, and W. Tholen: Closure operators II, inCategorical Topology and Its Relation to Analysis, Algebra and Combinatorics, Prague, 1988 (World Sci. Publ., New York, 1989), 297?335.
5. C. Dimitrovici, H. Ehrig, M. Gro�e-Rode, and C. Rieckhoff: Projektionsr�ume und Projektionsalgebren: Eine Algebraisierung von ultrametrischen R�umen, Technical Report 87-7, TU Berlin, 1987.