Published online by Cambridge University Press: 20 November 2018
Let V be a variety of rings and let A ∊ V. The ring A is injective in V if every triangle
with C ∊ V, m a monomorphism and f a homomorphism has a commutative completion as indicated. A ring which is injective in some variety (equivalently, injective in the variety it generates) is called injective. When only triangles with f surjective are considered we obtain the notion of weak injectivity. Directly indecomposable injective and weakly injective rings are classified.