1. A note on epi in T0;Baron;Canad. Math. Bull.,1968
2. Closure operators, monomorphisms and epimorphisms in categories of groups;Castellini;Cahiers Topologie Géom. Différentielle Catégoriques,1986
3. Global closure operators vs. subcategories;Castellini;Quaestiones Mathematicae,1990
4. Closure operators I;Dikranjan;Topology Appl.,1987
5. D. Dikranjan and E. Giuli, Preradicals, factorizations and compactness in categories of modules, Preprint.