1. P. N. Ánh, On Litoff's theorem,Studia Sci. Math. Hungar. 16 (1984), 255–259.Zbl 518: 16002
2. C. Faith, Rings with minimum condition on principal ideals,Arch. Math. 10 (1959), 327–330. [Erratum,Arch. Math. 10 (1959), 480.]MR 22: 719
3. O. Steinfeld,Quasi-ideals in rings and semigroups, Akadémiai Kiadó, Budapest, 1978.MR 80e: 16001
4. P. N. Stewart, Quasi-ideals in rings,Acta Math. Acad. Sci. Hungar. 38 (1981), 231–235.MR 83f: 16012
5. F. A. Szász, On minimal bi-ideals of rings,Acta Sci. Math. (Szeged)32 (1971), 333–336.MR 46: 5398