1. Auslander, M., Existence theorems for almost split sequences, in: Ring Theory II, Proceedings of the Second Oklahoma Conference (Norman 1975), pp. 1?44. New York-Basel, Marcel Dekker 1977
2. Auslander, M. and Reiten, I., Representation theory of Artin algebras IV, Comm. Algebra 5 (1977), 443?518
3. Bongartz, K. and Gabriel, P., Covering spaces in representation theory, Invent. Math. 65 (1982), 331?378
4. Dade, E.C., Some indecomposable group representations, Ann. of Math. (2) 77 (1963), 406?412
5. Drozd, Ju.A., Kirichenko, V.V. and Roiter, A.V., On hereditary and Bass orders, Izv. Akad. Nauk SSSR Ser. Mat. 31 (1967), 1415?1436=Math. USSR Izv. 1 (1967), 1357?1376