Adjoints of fully faithful functors #
A left adjoint is fully faithful, if and only if the unit is an isomorphism (and similarly for right adjoints and the counit).
Future work #
The statements from Riehl 4.5.13 for adjoints which are either full, or faithful.
If the left adjoint is fully faithful, then the unit is an isomorphism.
See
- Lemma 4.5.13 from [Riehl][riehl2017]
- https://math.stackexchange.com/a/2727177
- https://stacks.math.columbia.edu/tag/07RB (we only prove the forward direction!)
Equations
- ⋯ = ⋯
If the right adjoint is fully faithful, then the counit is an isomorphism.
See https://stacks.math.columbia.edu/tag/07RB (we only prove the forward direction!)
Equations
- ⋯ = ⋯
If the unit of an adjunction is an isomorphism, then its inverse on the image of L is given by L whiskered with the counit.
If the unit is an isomorphism, bundle one has an isomorphism L ⋙ R ⋙ L ≅ L
.
Equations
- h.whiskerLeftLCounitIsoOfIsIsoUnit = (L.associator R L).symm ≪≫ CategoryTheory.isoWhiskerRight (CategoryTheory.asIso h.unit).symm L ≪≫ L.leftUnitor
Instances For
If the counit of an adjunction is an isomorphism, then its inverse on the image of R is given by R whiskered with the unit.
If the counit of an is an isomorphism, one has an isomorphism (R ⋙ L ⋙ R) ≅ R
.
Equations
- h.whiskerLeftRUnitIsoOfIsIsoCounit = (R.associator L R).symm ≪≫ CategoryTheory.isoWhiskerRight (CategoryTheory.asIso h.counit) R ≪≫ R.leftUnitor
Instances For
If the unit is an isomorphism, then the left adjoint is fully faithful.
Equations
- One or more equations did not get rendered due to their size.
Instances For
If the counit is an isomorphism, then the right adjoint is fully faithful.
Equations
- One or more equations did not get rendered due to their size.
Instances For
Equations
- ⋯ = ⋯
Equations
- ⋯ = ⋯
Equations
- ⋯ = ⋯
Equations
- ⋯ = ⋯
Equations
- ⋯ = ⋯
Equations
- ⋯ = ⋯
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- ⋯ = ⋯
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- ⋯ = ⋯
If η_A
is an isomorphism, then A
is in the essential image of i
.
Alias of CategoryTheory.Adjunction.mem_essImage_of_unit_isIso
.
If η_A
is an isomorphism, then A
is in the essential image of i
.
Equations
- ⋯ = ⋯
Equations
- ⋯ = ⋯
Equations
- ⋯ = ⋯
Equations
- ⋯ = ⋯