Skip to main content
added 47 characters in body; edited title
Source Link
David Roberts
  • 35.4k
  • 11
  • 124
  • 348

When does the 2-category V-Cat have weak pullbackspseudo-pullbacks?

Edit: rewritten the question (edit:again), as I realised I wanted weak pullbacksweak pseudo-pullbacks, not comma objects.

Consider the 2-category $V$-$Cat$ of $V$-enriched categories. An example is $Cat$ itself, where we take $V=Cat$. I'm interested in the more general setting where $V$ is at least finitely complete and complete, if not possessing small limits and colimits outright. I also know that $V$ is such that small $V$-categories can be interpreted as categories internal to $V$ with object of objects given by a coproduct of the tensor unit.

Weak pullbacksPseudo-pullbacks exist in $Cat$, and can be calculated as a strict finite limit $A\times_C C^I \times_C B$ where $C^I$ is the isomorphism category of $C$. Actually I may not be interested in the weak pullbackspseudo-pullbacks, but pseudostrict 2-pullbacks, depending on what this example in $Cat$ is.

Based on Finn's answer, I guess this may exist when cotensors by $I$ exist ($I$ is the groupoid with two objects $a,b$ with a unique isomorphism $a \stackrel{\sim}{\to} b$). So this then is my question:

When do weakpseudo/pseudo pullbacksstrict 2-pullbacks (as appropriate) exist in $V$-$Cat$?

When does the 2-category V-Cat have weak pullbacks?

Edit: rewritten the question, as I realised I wanted weak pullbacks, not comma objects.

Consider the 2-category $V$-$Cat$ of $V$-enriched categories. An example is $Cat$ itself, where we take $V=Cat$. I'm interested in the more general setting where $V$ is at least finitely complete and complete, if not possessing small limits and colimits outright. I also know that $V$ is such that small $V$-categories can be interpreted as categories internal to $V$ with object of objects given by a coproduct of the tensor unit.

Weak pullbacks exist in $Cat$, and can be calculated as a strict finite limit $A\times_C C^I \times_C B$ where $C^I$ is the isomorphism category of $C$. Actually I may not be interested in the weak pullbacks, but pseudo-pullbacks, depending on what this example in $Cat$ is.

Based on Finn's answer, I guess this may exist when cotensors by $I$ exist ($I$ is the groupoid with two objects $a,b$ with a unique isomorphism $a \stackrel{\sim}{\to} b$). So this then is my question:

When do weak/pseudo pullbacks (as appropriate) exist in $V$-$Cat$?

When does the 2-category V-Cat have pseudo-pullbacks?

Edit: rewritten the question (edit:again), as I realised I wanted weak pseudo-pullbacks, not comma objects.

Consider the 2-category $V$-$Cat$ of $V$-enriched categories. An example is $Cat$ itself, where we take $V=Cat$. I'm interested in the more general setting where $V$ is at least finitely complete and complete, if not possessing small limits and colimits outright. I also know that $V$ is such that small $V$-categories can be interpreted as categories internal to $V$ with object of objects given by a coproduct of the tensor unit.

Pseudo-pullbacks exist in $Cat$, and can be calculated as a strict finite limit $A\times_C C^I \times_C B$ where $C^I$ is the isomorphism category of $C$. Actually I may not be interested in the pseudo-pullbacks, but strict 2-pullbacks, depending on what this example in $Cat$ is.

Based on Finn's answer, I guess this may exist when cotensors by $I$ exist ($I$ is the groupoid with two objects $a,b$ with a unique isomorphism $a \stackrel{\sim}{\to} b$). So this then is my question:

When do pseudo/strict 2-pullbacks (as appropriate) exist in $V$-$Cat$?

Rewrote question entirely
Source Link
David Roberts
  • 35.4k
  • 11
  • 124
  • 348

When does the 2-category V-Cat have comma objectsweak pullbacks?

QuestionEdit: rewritten the question, as in titleI realised I wanted weak pullbacks, not comma objects. The monoidal category

Consider the 2-category $V$-$Cat$ of $V$-enriched categories. An example is $Cat$ itself, where we take $V=Cat$. I'm interested in the more general setting where $V$ is at least finitely complete and cocompletecomplete, if not possessing small limits and cartesiancolimits outright. I also know that $V$ is such that small $V$-categories can be interpreted as categories internal to $V$ with object of objects given by a coproduct of the tensor unit.

Weak pullbacks exist in $Cat$, and can be calculated as a strict finite limit $A\times_C C^I \times_C B$ where $C^I$ is the isomorphism category of $C$. Actually I may not be interested in the weak pullbacks, but pseudo-pullbacks, depending on what this example in $Cat$ is.

Based on Finn's answer, I guess this may exist when cotensors by $I$ exist ($I$ is the groupoid with two objects $a,b$ with a unique isomorphism $a \stackrel{\sim}{\to} b$). So this then is my question:

When do weak/pseudo pullbacks (as appropriate) exist in $V$-$Cat$?

When does the 2-category V-Cat have comma objects?

Question as in title. The monoidal category $V$ I'm interested in is complete and cocomplete and cartesian

When does the 2-category V-Cat have weak pullbacks?

Edit: rewritten the question, as I realised I wanted weak pullbacks, not comma objects.

Consider the 2-category $V$-$Cat$ of $V$-enriched categories. An example is $Cat$ itself, where we take $V=Cat$. I'm interested in the more general setting where $V$ is at least finitely complete and complete, if not possessing small limits and colimits outright. I also know that $V$ is such that small $V$-categories can be interpreted as categories internal to $V$ with object of objects given by a coproduct of the tensor unit.

Weak pullbacks exist in $Cat$, and can be calculated as a strict finite limit $A\times_C C^I \times_C B$ where $C^I$ is the isomorphism category of $C$. Actually I may not be interested in the weak pullbacks, but pseudo-pullbacks, depending on what this example in $Cat$ is.

Based on Finn's answer, I guess this may exist when cotensors by $I$ exist ($I$ is the groupoid with two objects $a,b$ with a unique isomorphism $a \stackrel{\sim}{\to} b$). So this then is my question:

When do weak/pseudo pullbacks (as appropriate) exist in $V$-$Cat$?

Source Link
David Roberts
  • 35.4k
  • 11
  • 124
  • 348

When does the 2-category V-Cat have comma objects?

Question as in title. The monoidal category $V$ I'm interested in is complete and cocomplete and cartesian