structures in a cohesive (∞,1)-topos
infinitesimal cohesion?
In a context of synthetic differential geometry/differential cohesion the reduction modality characterizes reduced objects. It forms itself the left adjoint in an adjoint modality with the infinitesimal shape modality.
A context of differential cohesion is determined by the existence of an adjoint triple of modalities
where $Red$ and $\flat_{inf}$ are idempotent comonads and $ʃ_{inf}$ is an idempotent monad.
Here $Red$ is the reduction modality. The reflective subcategory that it defines is that of reduced objects.
(shape modality $\dashv$ flat modality $\dashv$ sharp modality)
$(ʃ \dashv \flat \dashv \sharp )$
(reduction modality $\dashv$ infinitesimal shape modality $\dashv$ infinitesimal flat modality)
$(Red \dashv ʃ_{inf} \dashv \flat_{inf})$