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wellpowered category (Definition)

Wellpoweredness is a kind of smallness condition on a category.

Let $ M$ be a class of monomorphisms. A category is said to be $ M$-wellpowered if for any object any class of parwise non-isomorphism $ M$-subobjects is a set. (By a $ M$-subobject of an object $ A$ we understand a pair $ (E,e)$, where $ e:E\to A$ is a morphism belonging to $ M$.) In other words, if we consider isomorphic objects as the same object, the class of all $ M$-subobjects is a set.

More precisely, for any $ A$ there exists a set of $ M$-subobjects $ (M_i,m_i)$, $ i\in I$ such that for any extremal subobject $ (M,m)$ of the object $ A$ there exists $ i\in I$ and an isomorphism $ f:M_i\to M$ such that $ m_i=m\circ f$.

If $ M$ is the class of all regular monomorphisms, extremal monomorphisms, monomorphisms, we speak about regular wellpowered, extremally wellpowered, wellpowered category.

Dual notions: regular cowellpowered, extremally cowellpowered, cowellpowered category.

Bibliography

1
J. Adámek, H. Herrlich, and G. Strecker.
Abstract and Concrete Categories.
Wiley, New York, 1990.



"wellpowered category" is owned by kompik.
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See Also: subobject

Other names:  wellpowered, well-powered, locally small
Also defines:  extremally wellpowered, regular wellpowered, cowellpowered, extremally cowellpowered, regulary cowellpowered
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Cross-references: regular, extremal monomorphisms, regular monomorphisms, isomorphism, subobject, isomorphic, morphism, object, monomorphisms, class, category
There are 5 references to this entry.

This is version 6 of wellpowered category, born on 2006-06-30, modified 2008-11-07.
Object id is 8113, canonical name is WellpoweredCategory.
Accessed 2719 times total.

Classification:
AMS MSC18A05 (Category theory; homological algebra :: General theory of categories and functors :: Definitions, generalizations)

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