Contents

# Contents

## Idea

A geometric hyperdoctrine is a hyperdoctrine with respect to lattices that are frames.

## Definition

Let $C$ be a category with finite limits. A geometric hyperdoctrine over $C$ is a functor

$P : C^{op} \to Frm$

from the opposite category of $C$ to the category of frames, such that for every morphism $f : A \to B$ in $C$, the functor $P(A) \to P(B)$ has a left adjoint $\exists_f$ satisfying

## Examples

Let $OLoc$ be the category of overt locales, and let $Frm$ be the category of frames. The functor $\mathcal{O}:OLoc^\op \to Frm$ that takes an overt locale to its frame of opens is a geometric hyperdoctrine.

Let $Set$ be the category of sets, defined as a Grothendieck topos on the singleton, and let $Frm$ be the category of frames. The subobject poset functor $\mathrm{Sub}:Set^\op \to Frm$ that takes a set to its subobject poset is a geometric hyperdoctrine.

This could be generalized to any geometric category $C$: the subobject poset functor $\mathrm{Sub}:C^\op \to Frm$ that takes an object of $C$ to its subobject poset is a geometric hyperdoctrine.