Projective S-acts and Exact Functors
Yuqun Chen · Algebra Colloquium · 2000
Let S be a semigroup. In this paper, projective S -acts and exact sequences in S -Act are studied. It is shown that, for a unitary S -act P , the functor Hom( P , –) is exact if and only if P ≅ Se for some idempotent e ɛ S .