CatDat

representable

A functor $F : \C \to \D$ is representable if $\C$ is locally small, $\D = \Set$, and there is an object $A \in \C$ with $F \cong \Hom(A,-)$.

• Related properties: continuous
• nLab Link

Relevant implications

• representable implies continuous

Examples

There are 9 functors with this property.

• binary product functor on sets
• contravariant power set functor
• forgetful functor for groups
• forgetful functor for rings
• forgetful functor for topological spaces
• forgetful functor for vector spaces
• identity functor on the category of sets
• sequences functor on sets
• squaring functor on sets

Counterexamples

There are 18 functors without this property.

• abelianization functor for groups
• binary coproduct functor on sets
• binary diagonal functor on the category of sets
• countable copower functor on sets
• covariant power set functor
• discrete topology functor
• doubling functor on sets
• enveloping group functor
• forgetful functor from abelian groups to groups
• forgetful functor from groups to monoids
• forgetful functor from rings to monoids
• free group functor
• functor of continuous functions
• group of units functor
• modulo p functor
• monoid ring functor
• p-torsion functor
• torsion functor

Unknown

There are 0 functors for which the database has no information on whether they satisfy this property.

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