1. Ferrero, M. Unitary strongly prime rings and ideals. Proceedings of the 35th Symposium on Ring Theory and Representation Theory (Okayama, 2002), 101–111, Symp. Ring Theory Representation Theory Organ. Comm., Okayama, 2003.
2. Ferrero, M.; Wisbauer, R. Unitary strongly prime rings and related radicals. J. Pure Appl. Algebra 181 (2003), 209–226.
3. Krempa, J. Logical connections among some open problems in non-commutative rings. Fund. Math. 76 (1972), 121–130.
4. Colloq. Math. Soc. Janos Bolyai;E.R. Puczyłowski,1993
5. Puczyłowski, E.R. Some results and questions on nil rings. 15th School of Algebra (Portuguese) (Canela, 1998). Mat. Contemp. 16 (1999), 265–280.