Adámek, Jiří; El Bashir, Robert; Sobral, Manuela; Jiří, Velebil

On functors which are lax epimorphisms

Theory Appl. Categ. 8, 509-521, electronic only (2001)


Summary: We show that lax epimorphisms in the category Cat are precisely the functors $P : {\cal E} \to {\cal B}$ for which the functor $P^{*}: [{\cal B}, Set] \to [{\cal E}, Set]$ of composition with $P$ is fully faithful. We present two other characterizations. Firstly, lax epimorphisms are precisely the "absolutely dense" functors, i.e., functors $P$ such that every object $B$ of ${\cal B}$ is an absolute colimit of all arrows $P(E)\to B$ for $E$ in ${\cal E}$. Secondly, lax epimorphisms are precisely the functors $P$ such that for every morphism $f$ of ${\cal B}$ the category of all factorizations through objects of $P[{\cal E}]$ is connected.

Mathematics Subject Classification



Lax epimorphism