If $R$ is a prime ring such that $R$ is not completely reducible and the additive group $R(+)$ is not complete, then $R$ is slender.
@article{118847, author = {Robert El Bashir and Tom\'a\v s Kepka}, title = {Notes on slender prime rings}, journal = {Commentationes Mathematicae Universitatis Carolinae}, volume = {37}, year = {1996}, pages = {419-422}, zbl = {0854.16016}, mrnumber = {1399017}, language = {en}, url = {http://dml.mathdoc.fr/item/118847} }
El Bashir, Robert; Kepka, Tomáš. Notes on slender prime rings. Commentationes Mathematicae Universitatis Carolinae, Tome 37 (1996) pp. 419-422. http://gdmltest.u-ga.fr/item/118847/
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