1. V. A. Andrunakievič, Radicals in associative rings. I,Mat. Sb.,44 (1958), 179–212 (in Russian);Amer. Math. Soc. Transl.,52 (2) (1966), 95–128.
2. V. A. Andrunakievič, Radicals in associative rings. II,Mat. Sb.,55 (1961), 329–346 (in Russian);Amer. Math. Soc. Transl.,52 (2) (1966), 129–149.
3. R. Baer, Radical ideals,Amer. J. Math.,65 (1943), 537–568.
4. C. W. Curtis, A note on noncommutative polynomials,Proc. Amer. Math. Soc.,3 (1952), 965–969.
5. N. Divinsky,Rings and Radicals, Univ. of Toronto Press (1965).