CatDat

left adjoint

A functor $F : \mathcal{C} \to \mathcal{D}$ is a left adjoint when there is a functor $G : \mathcal{D} \to \mathcal{C}$ such that there are natural bijections $\hom(F(A),B) \cong \hom(A,G(B))$.

• Dual property: right adjoint
• nLab Link

Relevant implications

• cocontinuous implies left adjoint *
• comonadic implies conservative andfaithful andleft adjoint
• equivalence implies cocontinuous andcomonadic andleft adjoint
• left adjoint implies cocontinuous

*Those implications also require assumptions on the source or target category.

Examples

There are 3 functors with this property.

• abelianization functor for groups
• free group functor
• identity functor on the category of sets

Counterexamples

There are 3 functors without this property.

• contravariant power set functor
• covariant power set functor
• forgetful functor for vector spaces

Unknown

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

—