Balanced category
In mathematics, especially in category theory, a balanced category is a category in which every bimorphism (a morphism that is both a monomorphism and epimorphism) is an isomorphism.
The category of topological spaces is not balanced (since continuous bijections are not necessarily homeomorphisms), while a topos is balanced.[1] This is one of the reasons why a topos is said to be nicer.[2]
Examples[edit]
The following categories are balanced
- Set, the category of sets.
- An abelian category.[3]
- The category of (Hausdorff) compact spaces (since a continuous bijection there is homeomorphic).
An additive category may not be balanced.[4] Contrary to what one might expect, a balanced pre-abelian category may not be abelian.[5]
A quasitopos is similar to a topos but may not be balanced.
See also[edit]
References[edit]
- ^ Johnstone 1977
- ^ "On a Topological Topos at The n-Category Café". golem.ph.utexas.edu.
- ^ A brief introduction to abelian categories
- ^ "Is an additive category a balanced category?". MathOverflow.
- ^ "Is every balanced pre-abelian category abelian?". MathOverflow.
- P.T. Johnstone,"Topos theory", Academic Press (1977)
- Roy L. Crole, Categories for types, Cambridge University Press (1994)
Further reading[edit]
- balanced category at the nLab
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