The concept of a codense functor is the dual of dense functor.
Let be a functor between categories. It is codense when for each the following is true:
(where is a comma category (in this case the under category) from to the functor .
This notion is dual to the notion of dense functor.
Equivalently, a functor is codense iff , together with identity natural transformation , is the pointwise right Kan extension, , of along .
Also, is codense iff its codensity monad is the identity.
A subcategory is codense if the inclusion functor is codense.
Friedrich Ulmer, Properties of Dense and Relative Adjoint Functors, Journal of Algebra 8, 77-95 (1968)
William Lawvere, John Isbell’s Adequate Subcategories, TopCom 11 no.1 2006. (link)
Last revised on August 25, 2024 at 21:44:38. See the history of this page for a list of all contributions to it.