category of countable sets
A set is countable if it admits a surjection from . In particular, every finite set is countable.
Satisfied Properties
Assigned properties
- is locally small
- is essentially small
- is finitely complete
- is finitely cocomplete
- has a subobject classifier
- is epi-regular
- has a generator
- has a cogenerator
- is semi-strongly connected
- is extensive
- is countably distributive
- has effective congruences
- is regular
- is coregular
Deduced properties
- has a natural numbers object
- has equalizers
- has finite products
- has quotients of congruences
- is co-Malcev
- has effective cocongruences
- is mono-regular
- is Barr-exact
- is connected
- has countable coproducts
- is distributive
- has finite coproducts
- has disjoint finite coproducts
- has a strict initial object
- is filtered
- has a generating set
- is inhabited
- is locally essentially small
- is well-copowered
- is well-powered
- has a regular subobject classifier
- has coequalizers
- is cofiltered
- has a cogenerating set
- is balanced
- has coreflexive equalizers
- is Cauchy complete
- is sifted
- is ℵ₁-filtered
- has an initial object
- has binary products
- has a terminal object
- has finite powers
- is a pretopos
- has coquotients of cocongruences
- is Barr-coexact
- has reflexive coequalizers
- is cosifted
- has sequential colimits
- has binary coproducts
- has countable copowers
- has finite copowers
- is accessible
- has a multi-terminal object
- has binary powers
- has pullbacks
- is coaccessible
- has a multi-initial object
- is ℵ₁-cofiltered
- has binary copowers
- has pushouts
Unsatisfied Properties
Assigned properties
- is not small
- is not skeletal
- does not have countable powers
- does not have ℵ₂-small copowers
- does not have ℵ₁-cofiltered limits
Deduced properties*
- is not cartesian closed
- is not discrete
- does not have countable products
- does not have ℵ₂-small powers
- does not have sequential limits
- is not gaunt
- is not direct
- does not have cofiltered limits
- does not have ℵ₂-small coproducts
- does not have copowers
- is not inverse
- is not self-dual
- is not locally cartesian closed
- is not trivial
- does not have directed limits
- is not a groupoid
- does not have ℵ₂-small products
- does not have powers
- does not have filtered colimits
- does not have ℵ₁-filtered colimits
- does not have wide pullbacks
- is not an elementary topos
- is not countably codistributive
- does not have exact cofiltered limits
- does not have cocartesian cofiltered limits
- does not have cofiltered-limit-stable epimorphisms
- is not essentially finite
- does not have cosifted limits
- does not have coproducts
- is not thin
- is not pointed
- is not ℵ₁-accessible
- is not finitely accessible
- is not locally poly-presentable
- is not Grothendieck abelian
- is not right cancellative
- is not left cancellative
- is not essentially discrete
- does not have disjoint coproducts
- does not have a strict terminal object
- is not infinitary distributive
- does not have exact filtered colimits
- does not have cartesian filtered colimits
- does not have filtered-colimit-stable monomorphisms
- does not satisfy CIP
- is not infinitary extensive
- does not have directed colimits
- does not have sifted colimits
- does not have products
- does not have connected limits
- is not finite
- is not additive
- is not subobject-trivial
- is not core-thin
- is not a Grothendieck topos
- is not cocartesian coclosed
- is not cocomplete
- does not have disjoint finite products
- is not infinitary codistributive
- does not satisfy CSP
- does not have wide pushouts
- does not have a regular quotient object classifier
- is not quotient-trivial
- is not locally finite
- is not essentially countable
- is not unital
- is not locally finitely presentable
- is not locally ℵ₁-presentable
- is not locally presentable
- is not locally strongly finitely presentable
- is not locally multi-presentable
- is not locally finitely multi-presentable
- is not preadditive
- is not abelian
- is not a generalized variety
- is not complete
- is not strongly connected
- does not have connected colimits
- does not have zero morphisms
- is not countable
- is not Malcev
- is not one-way
- is not counital
- is not locally copresentable
- is not locally cocartesian coclosed
- is not multi-cocomplete
- does not have disjoint products
- is not codistributive
- is not infinitary coextensive
- is not coextensive
- does not have a quotient object classifier
- does not have biproducts
- is not split abelian
- is not finitary algebraic
- is not multi-algebraic
- is not multi-complete
- does not have kernels
- is not normal
- does not have cokernels
- is not conormal
*This also uses the deduced satisfied properties.
Unknown properties
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Special objects
- terminal object: singleton set
- initial object: empty set
- products: [finite case] direct products
- coproducts: [countable case] disjoint union
Special morphisms
- isomorphisms: bijective maps
- monomorphisms: injective maps
- epimorphisms: surjective maps
- regular monomorphisms: same as monomorphisms
- regular epimorphisms: same as epimorphisms