A ring is called a commutator ring if every element is a sum of additive commutators. In this note we give examples of such rings. In particular, we show that given any ring R, a right R-module N, and a nonempty set Ω, End_R(?_ΩN) and End_R(Π_Ω N) are commutator rings if and only if either ΩN is infinite or End_R(N) is itself a commutator ring. We also prove that over any ring, a matrix having trace zero can be expressed as a sum of two commutators.
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