1. F. W. Anderson and K. R. Fuller, Rings and Categories of Modules, Springer, New York - Heidelberg - Berlin, 1974.
2. H. Bass, Algebraic K-theory, W. A. Benjamin, Inc., New York-Amsterdam, 1968.
3. I. N. Bernšteĭn, I. M. Gelfand, and V. A. Ponomarev, Coxeter functors, and Gabriel’s theorem, Uspehi Mat. Nauk 28 (1973), 19-33.
4. K. Bongartz and P. Gabriel, Covering spaces in representation-theory, Invent. Math. 65 (1981/82), 331-378.
5. J. A. Drozd and V. V. Kiričenko, On quasi-Bass orders, Izv. Akad. Nauk SSSR 36 (1972), 328-370.