1. Andrunakievič, V.A.-Ju. M. Rjabukhin,Modules and radicals (in Russian), Doklady Akad. Nauk. SSSR 156 (1964), 991–994.
2. Colloq. Math. Soc. J. Bolyai;Biro,1977
3. Clifford, A.H.-G.B. Preston,The algebraic theory of semigroups, I, Amer. Math. Soc., Providence, 1961.
4. Dickson, S.E.,A torsion theory for abelian categories, Trans. Amer. Math., Soc. 121 (1966), 223–235.
5. Fried, E.-R. Wiegandt,Connectednesses and disconnectednesses of graphs, Algebra Universalis 5 (1975), 411–428.