countable powers
A category has countable powers when for every object and every countable set the power exists.
- Dual property: countable copowers
- Related properties: countable products, finite powers, powers
- nLab Link
Relevant implications
- cartesian closed andcountable copowers implies countable powers
- countable copowers andself-dual implies countable powers
- countable powers andself-dual implies countable copowers
- countable powers implies finite powers
- countable products implies countable powers
- finite powers andsequential limits implies countable powers
- powers implies countable powers
Examples
There are 42 categories with this property.
- category of abelian groups
- category of abelian sheaves
- category of algebras
- category of Banach spaces with linear contractions
- category of commutative algebras
- category of commutative monoids
- category of commutative rings
- category of groups
- category of Hausdorff spaces
- category of left modules over a division ring
- category of left modules over a ring
- category of locally ringed spaces
- category of M-sets
- category of measurable spaces
- category of metric spaces with continuous maps
- category of metric spaces with ∞ allowed
- category of monoids
- category of non-empty sets
- category of pairs of sets
- category of pointed sets
- category of pointed topological spaces
- category of posets
- category of prosets
- category of rings
- category of rngs
- category of sets
- category of sets and relations
- category of sheaves
- category of simplicial sets
- category of small categories
- category of topological spaces
- category of vector spaces
- category of Z-functors
- dual of the category of sets
- poset [0,1]
- poset of extended natural numbers
- proset of integers w.r.t. divisibility
- trivial category
- walking commutative square
- walking composable pair
- walking isomorphism
- walking morphism
Counterexamples
There are 22 categories without this property.
- category of fields
- category of finite abelian groups
- category of finite orders
- category of finite sets
- category of finite sets and bijections
- category of finite sets and injections
- category of finite sets and surjections
- category of finitely generated abelian groups
- category of free abelian groups
- category of schemes
- delooping of a non-trivial finite group
- delooping of an infinite group
- delooping of the additive monoid of natural numbers
- delooping of the additive monoid of ordinal numbers
- discrete category on two objects
- empty category
- poset of natural numbers
- poset of ordinal numbers
- walking fork
- walking idempotent
- walking parallel pair
- walking span
Unknown
There are 3 categories for which the database has no information on whether they satisfy this property. Please help us fill in the gaps by contributing to this project.