1. L. Fuchs,Infinite abelian groups, I and II, Academic Press (1970 and 1973).
2. B. J. Gardner, Radicals and left ideals,Bull. Acad. Polon. Sci.,24 (1976), 943–945.
3. R. A. Good andD. R. Hughes, Associated groups for a semigroup,Bull. Amer. Math. Soc.,58 (1952), 624–625.
4. S. Lajos andF. Szász, On (m, n)-ideals in associative rings,Publ. Math. Debrecen,25 (1978), 265–273.
5. L. Rédei,Algebra I, Pergamon Press (1967).