Neat-phantom and clean-cophantom morphisms

L Mao - Journal of Algebra and Its Applications, 2021 - World Scientific
L Mao
Journal of Algebra and Its Applications, 2021World Scientific
Let ℱ 𝒫∞ R be the class of all left R-modules M which has a projective resolution by finitely
generated projectives. An exact sequence 0→ A→ B→ C→ 0 of right R-modules is called
neat if the sequence 0→ A⊗ RG→ B⊗ RG→ C⊗ RG→ 0 is exact for any G∈ ℱ 𝒫∞ R. An
exact sequence 0→ M→ N→ L→ 0 of left R-modules is called clean if the sequence 0→
Hom R (G, M)→ Hom R (G, N)→ Hom R (G, L)→ 0 is exact for any G∈ ℱ 𝒫∞ R. We prove
that every R-module has a clean-projective precover and a neat-injective envelope. A …
Let be the class of all left -modules which has a projective resolution by finitely generated projectives. An exact sequence of right -modules is called neat if the sequence is exact for any . An exact sequence of left -modules is called clean if the sequence 0 →HomR(G,M) →HomR(G,N) →HomR(G,L) → 0 is exact for any . We prove that every -module has a clean-projective precover and a neat-injective envelope. A morphism of right -modules is called a neat-phantom morphism if for any . A morphism of left -modules is said to be a clean-cophantom morphism if for any . We establish the relationship between neat-phantom (respectively, clean-cophantom) morphisms and neat (respectively, clean) exact sequences. Also, we prove that every -module has a neat-phantom cover with kernel neat-injective and a clean-cophantom preenvelope with cokernel clean-projective.
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