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Todd Trimble
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In Johnstone's book Topos Theory, he mentions an unresolved problem as to whether the 2-category $\mathbf{\text{Top}}$$\mathbf{\text{Topos}}$ of Grothendieck toposes and geometric morphisms admits pseudo-colimits. $\mathbf{\text{Top}}$$\mathbf{\text{Topos}}$ does admit lax colimits (including, famously, examples of Artin-Wraith gluing), and he remarks that insofar as

$$\mathbf{\text{Top}}^{op} \to Cat$$$$\mathbf{\text{Topos}}^{op} \to Cat$$

(which you can think of as the forgetful 2-functor from from Grothendieck toposes and left exact left adjoints to categories and functors) is represented by the object classifier $Set^{Fin}$, hence takes pseudo-colimits in $\mathbf{\text{Top}}$$\mathbf{\text{Topos}}$ to pseudo-limits in $Cat$, what we are really asking is whether a pseudo-limit in $Cat$ of toposes and lex left adjoints gives back a topos.

Johnstone's book was written a long time ago, and I was wondering whether there has been progress on this problem since then.

In Johnstone's book Topos Theory, he mentions an unresolved problem as to whether the 2-category $\mathbf{\text{Top}}$ of Grothendieck toposes and geometric morphisms admits pseudo-colimits. $\mathbf{\text{Top}}$ does admit lax colimits (including, famously, examples of Artin-Wraith gluing), and he remarks that insofar as

$$\mathbf{\text{Top}}^{op} \to Cat$$

(which you can think of as the forgetful 2-functor from from Grothendieck toposes and left exact left adjoints to categories and functors) is represented by the object classifier $Set^{Fin}$, hence takes pseudo-colimits in $\mathbf{\text{Top}}$ to pseudo-limits in $Cat$, what we are really asking is whether a pseudo-limit in $Cat$ of toposes and lex left adjoints gives back a topos.

Johnstone's book was written a long time ago, and I was wondering whether there has been progress on this problem since then.

In Johnstone's book Topos Theory, he mentions an unresolved problem as to whether the 2-category $\mathbf{\text{Topos}}$ of Grothendieck toposes and geometric morphisms admits pseudo-colimits. $\mathbf{\text{Topos}}$ does admit lax colimits (including, famously, examples of Artin-Wraith gluing), and he remarks that insofar as

$$\mathbf{\text{Topos}}^{op} \to Cat$$

(which you can think of as the forgetful 2-functor from from Grothendieck toposes and left exact left adjoints to categories and functors) is represented by the object classifier $Set^{Fin}$, hence takes pseudo-colimits in $\mathbf{\text{Topos}}$ to pseudo-limits in $Cat$, what we are really asking is whether a pseudo-limit in $Cat$ of toposes and lex left adjoints gives back a topos.

Johnstone's book was written a long time ago, and I was wondering whether there has been progress on this problem since then.

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Todd Trimble
  • 53.3k
  • 6
  • 205
  • 322

In Johnstone's book Topos Theory, he mentions an unresolved problem as to whether the 2-category $\mathbf{\text{Top}}$ of Grothendieck toposes and geometric morphisms admits pseudo-colimits. $\mathbf{\text{Top}}$ does admit lax colimits (including, famously, examples of Artin-Wraith gluing), and he remarks that insofar as

$$\mathbf{\text{Top}}^{op} \to Cat$$

(which you can think of as the forgetful 2-functor from from Grothendieck toposes and left exact left adjoints to categories and functors) is represented by the object classifier $Set^{Fin^{op}}$$Set^{Fin}$, hence takes pseudo-colimits in $\mathbf{\text{Top}}$ to pseudo-limits in $Cat$, what we are really asking is whether a pseudo-limit in $Cat$ of toposes and lex left adjoints gives back a topos.

Johnstone's book was written a long time ago, and I was wondering whether there has been progress on this problem since then.

In Johnstone's book Topos Theory, he mentions an unresolved problem as to whether the 2-category $\mathbf{\text{Top}}$ of Grothendieck toposes and geometric morphisms admits pseudo-colimits. $\mathbf{\text{Top}}$ does admit lax colimits (including, famously, examples of Artin-Wraith gluing), and he remarks that insofar as

$$\mathbf{\text{Top}}^{op} \to Cat$$

(which you can think of as the forgetful 2-functor from from Grothendieck toposes and left exact left adjoints to categories and functors) is represented by the object classifier $Set^{Fin^{op}}$, hence takes pseudo-colimits in $\mathbf{\text{Top}}$ to pseudo-limits in $Cat$, what we are really asking is whether a pseudo-limit in $Cat$ of toposes and lex left adjoints gives back a topos.

Johnstone's book was written a long time ago, and I was wondering whether there has been progress on this problem since then.

In Johnstone's book Topos Theory, he mentions an unresolved problem as to whether the 2-category $\mathbf{\text{Top}}$ of Grothendieck toposes and geometric morphisms admits pseudo-colimits. $\mathbf{\text{Top}}$ does admit lax colimits (including, famously, examples of Artin-Wraith gluing), and he remarks that insofar as

$$\mathbf{\text{Top}}^{op} \to Cat$$

(which you can think of as the forgetful 2-functor from from Grothendieck toposes and left exact left adjoints to categories and functors) is represented by the object classifier $Set^{Fin}$, hence takes pseudo-colimits in $\mathbf{\text{Top}}$ to pseudo-limits in $Cat$, what we are really asking is whether a pseudo-limit in $Cat$ of toposes and lex left adjoints gives back a topos.

Johnstone's book was written a long time ago, and I was wondering whether there has been progress on this problem since then.

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Todd Trimble
  • 53.3k
  • 6
  • 205
  • 322

Does the 2-category of toposes admit pseudo-colimits?

In Johnstone's book Topos Theory, he mentions an unresolved problem as to whether the 2-category $\mathbf{\text{Top}}$ of Grothendieck toposes and geometric morphisms admits pseudo-colimits. $\mathbf{\text{Top}}$ does admit lax colimits (including, famously, examples of Artin-Wraith gluing), and he remarks that insofar as

$$\mathbf{\text{Top}}^{op} \to Cat$$

(which you can think of as the forgetful 2-functor from from Grothendieck toposes and left exact left adjoints to categories and functors) is represented by the object classifier $Set^{Fin^{op}}$, hence takes pseudo-colimits in $\mathbf{\text{Top}}$ to pseudo-limits in $Cat$, what we are really asking is whether a pseudo-limit in $Cat$ of toposes and lex left adjoints gives back a topos.

Johnstone's book was written a long time ago, and I was wondering whether there has been progress on this problem since then.