The submodule in its injective hull is small } is investigated by Talebi und Vanaja (Citation2002) for every R-module M. We solve the three problems which were put forth in that work by replacing the submodule
over every commutative Noetherian ring R by the submodule C(M) = ∩ {U ⊂ M | M/U is cosingular }, which is easier to calculate. We give criteria for M/C (M) being cosingular or C
2 (M) = C
3 (M), respectively. Every R-module M satisfies
and we characterise those rings R over which
.
Notes
#Communicated by A. Facchini.