@lingyuan If it's elementary, I certainly hadn't realised the full depth of that connection! Bravo!

@lingyuan Hi, bit late to the party again, and Jens has already shown how we can syntactically prove your sequent using the rules of geometric logi...

New link to the toposes online gather town room: This should remain valid for the remainder of the talk, let me know if there's any problems.

Hi all, good to see there is interest in hosting another gathertown. Let's proceed as follows: I will post another invite link this afternoon if ...

This looks a lot like the construction of a geometric morphism from a functor given on pages 358-359 of Sheaves in Geometry and Logic by MacLane and...

Hi, I don't have much to add as you're post is very clear. I very much like the "union and covering" description - it points towards the very geome...

@lingyuan Hi Lingyuan, Thank you for the interesting question! I've been thinking about this insight for a while now, and I think I'm now in a po...

Hi again, I never said fuzzy set theory and standard set theory are semantically equivalent. The two topoi and are definitely not equivalent catego...

Hi there, correct me if I'm wrong but what it sounds like you're describing is a sort of interpretability of signatures. Fortunately for topos theory...

Hi all, attached are some updated notes representing some work that myself and Jens have been conducting behind the scenes. It includes a corrected v...

Indeed, had I read further in TST, I would have come across the very result I proved in the attachment above in Subsection 4.2.2.4, therein described ...

Hi again, I've attached the notes promised in the post above. Let me know if there's any mistakes. Otherwise, this gives necessary and sufficient co...

Hi Jens, coincidentally I have been working on the reverse implication too. The result I have is the same: that if and only if (i.e. the action is...