Corrected a silly error in the title.

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edited Oct 22, 2012 at 7:45

Jonathan Chiche

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Is there a standard name for a 2-category which has an object z such that, for every object x, the category Hom(x,z) has a terminal object?

Title shortened and LaTeX removed from it, added final remark.

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edited Oct 22, 2012 at 7:28

Jonathan Chiche

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Is there a standard name for an object $z$ of a 2-category such that, for every object $x$x, the category $HomHom(x,z)$ has a terminal object? Do 2-categories which admit such an object appear naturally elsewhere?

There are two distinct but related questions here. Since the first one is a terminological one, which certainly is not that interesting, I am asking both of them at the same time.

Motivation

In Pursuing Stacks, Grothendieck defines what he calls a basic localizer, which is, to put it roughly, a class of functors between small categories with which one can make homotopy in $Cat$. One axiom of basic localizers asserts that every category which has a terminal object is "aspherical", i.e. the canonical arrow from it to the point is in any basic localizer. Of course, this is something required, and itIt is a sufficient condition to get all the properties we want, provided the other axioms hold.

I have recently worked on "2-basic localizers", the analogous classes of (let say strict for convenience) 2-functors. It appears that what seems, from this viewpoint, the right analogous notion of "category with terminal object" is "2-category which has an object $z$ such that, given any object $x$, the category $Hom (x,z)$ has a terminal object". Instances of such 2-categories are "slices over an object". (There are, of course, three dual notions, the four of them corresponding to the two ways to slice over an object and the two ways to slice under an object.)

Question 1

Does this property have a standard name?

I am aware that there should be something like an adjunction between such a 2-category and the terminal one going on here, but I am really looking for standard terminology if there is one now.

Question 2

Do this kind of 2-categories or this kind of property appear naturally in other contexts?

This second question may be as silly as asking "where do categories with a terminal object crop up", but category theorists I have talked to do not seem to have encountered such a notion. I hope it could ring a bell for other people, especially those working on homotopy-related stuff.

EDIT: To be a bit more precise, I have the feeling that this property has something to do with prefibrations in $2-Cat$. Perhaps I will tell more about that later.

Is there a standard name for an object $z$ of a 2-category such that, for every object $x$, the category $Hom(x,z)$ has a terminal object? Do 2-categories which admit such an object appear naturally elsewhere?

There are two distinct but related questions here. Since the first one is a terminological one, which certainly is not that interesting, I am asking both of them at the same time.

Motivation

In Pursuing Stacks, Grothendieck defines what he calls a basic localizer, which is, to put it roughly, a class of functors between small categories with which one can make homotopy in $Cat$. One axiom of basic localizers asserts that every category which has a terminal object is "aspherical", i.e. the canonical arrow from it to the point is in any basic localizer. Of course, this is something required, and it is a sufficient condition provided the other axioms hold.

I have recently worked on "2-basic localizers", the analogous classes of (let say strict for convenience) 2-functors. It appears that what seems the right analogous notion of "category with terminal object" is "2-category which has an object $z$ such that, given any object $x$, the category $Hom (x,z)$ has a terminal object". Instances of such 2-categories are "slices over an object". (There are, of course, three dual notions, the four of them corresponding to the two ways to slice over an object and the two ways to slice under an object.)

Question 1

Does this property have a standard name?

I am aware that there should be something like an adjunction between such a 2-category and the terminal one going on here, but I am really looking for standard terminology if there is one now.

Question 2

Do this kind of 2-categories or this kind of property appear naturally in other contexts?

This second question may be as silly as asking "where do categories with a terminal object crop up", but category theorists I have talked to do not seem to have encountered such a notion. I hope it could ring a bell for other people, especially those working on homotopy-related stuff.

Is there a standard name for a 2-category such that, for every object x, the category Hom(x,z) has a terminal object?

Motivation

In Pursuing Stacks, Grothendieck defines what he calls a basic localizer, which is, to put it roughly, a class of functors between small categories with which one can make homotopy in $Cat$. One axiom of basic localizers asserts that every category which has a terminal object is "aspherical", i.e. the canonical arrow from it to the point is in any basic localizer. It is a sufficient condition to get all the properties we want, provided the other axioms hold.

I have recently worked on "2-basic localizers", the analogous classes of (let say strict for convenience) 2-functors. It appears that what seems, from this viewpoint, the right analogous notion of "category with terminal object" is "2-category which has an object $z$ such that, given any object $x$, the category $Hom (x,z)$ has a terminal object". Instances of such 2-categories are "slices over an object". (There are, of course, three dual notions, the four of them corresponding to the two ways to slice over an object and the two ways to slice under an object.)

Question 1

Does this property have a standard name?

I am aware that there should be something like an adjunction between such a 2-category and the terminal one going on here, but I am really looking for standard terminology if there is one now.

Question 2

Do this kind of 2-categories or this kind of property appear naturally in other contexts?

This second question may be as silly as asking "where do categories with a terminal object crop up", but category theorists I have talked to do not seem to have encountered such a notion. I hope it could ring a bell for other people, especially those working on homotopy-related stuff.

EDIT: To be a bit more precise, I have the feeling that this property has something to do with prefibrations in $2-Cat$. Perhaps I will tell more about that later.

Going back to the original title. See my comments.

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edited Sep 29, 2012 at 23:43

Jonathan Chiche

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Naming Is there a standard name for an object $z$ of a 2-category such that, for every object $x$, the category $Hom(x,z)$ has a terminal object.? Do 2-categories which admit such an object appear naturally elsewhere?

edited title; edited title

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edited Sep 29, 2012 at 13:41

Andrej Bauer

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deleted 60 characters in body; edited title

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edited Sep 29, 2012 at 12:33

Jonathan Chiche

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asked Sep 29, 2012 at 9:10

Jonathan Chiche

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Is there a standard name for a 2-category which has an object z such that, for every object x, the category Hom(x,z) has a terminal object?

Is there a standard name for an object $z$ of a 2-category such that, for every object $x$x, the category $HomHom(x,z)$ has a terminal object? Do 2-categories which admit such an object appear naturally elsewhere?

Is there a standard name for an object $z$ of a 2-category such that, for every object $x$, the category $Hom(x,z)$ has a terminal object? Do 2-categories which admit such an object appear naturally elsewhere?

Is there a standard name for a 2-category such that, for every object x, the category Hom(x,z) has a terminal object?

Naming Is there a standard name for an object $z$ of a 2-category such that, for every object $x$, the category $Hom(x,z)$ has a terminal object.? Do 2-categories which admit such an object appear naturally elsewhere?