Mittag-Leffler modules, reduced products, and direct products
For every module we have a natural monomorphism and we focus our attention on the case when is also an epimorphism. Some other colimits are also considered.
For every module M we have a natural monomorphism and we focus attention on the case when Φ is also an epimorphism. The corresponding modules M depend on thickness of the cardinal number card(I). Some other limits are also considered.
We study the class of modules which are invariant under idempotents of their envelopes. We say that a module M is -idempotent-invariant if there exists an -envelope u : M → X such that for any idempotent g ∈ End(X) there exists an endomorphism f : M → M such that uf = gu. The properties of this class of modules are discussed. We prove that M is -idempotent-invariant if and only if for every decomposition , we have . Moreover, some generalizations of -idempotent-invariant modules are considered....