Statement: Let U be a simple right R module, and D be the ring of endomorphisms of U. If A is any D linear operator and X is any finite subset of R, there exists r in R such that xr=xA for all x in X.

Link: https://en.wikipedia.org/wiki/Jacobson_density_theorem

- Isaacs, I. Martin, Algebra: A Graduate Course., Brooks/Cole Publishing Company, (1994). Theorem 13.14 P 185