Abstract. In this paper we note some properties of fully invariant additive subgroups of near-rings and apply these results to d.g., medial, or subdirectly irreducible near-rings. This extends the results in our paper: "Medial Near-Rings", Mh. Math. 107, 89--110 (1989).In this paper we show that fully invariant additive groups play a role in the structure of near-rings, especially d.g. near-rings. Properties of these additive groups are then used to obtain results about d.g., medial, or subdirectly irreducible near-rings or near-rings whose additive group is locally nilpotent. This extends results in [1]. We also correct some minor errors found in [1]. The notation and terminology herein are the same as that used in our previous paper on medial near-tings [1].
Proposition 1. Let R be a near-ring and let S be a fully invariant subgroup of R +. Then: O) S is a left ideal of R and S (ngp (9 (R))) ___ S; (ii) If[R, R] c_ S, then S is an ideal of R and is' a right R-subgroup; (iii) If R is d.g., then S is an ideal of R.Proof For any e E R, de N (R), the mappings x ~ e x and x ~ x d are endomorphisms on R +. Thus S is a left ideal of R and S (9 (R)) ___ S; since S is normal in R + this yields S (ngp (9 (R))) __c S. From Proposition 2.1 (iii) of [1] we have that [R, R] _c S and S a left ideal implies S is an ideal and a right R-subgroup. If R is d.g., the gp (9 (R)) = R and every normal right R-subgroup is a tight ideal. So (i) yields (iii) immediately.