nLab
anti-reduced type

Contents

Context

Cohesion

cohesive topos

cohesive (∞,1)-topos

cohesive homotopy type theory

Backround

Definition

Presentation over a site

Structures in a cohesive (,1)(\infty,1)-topos

structures in a cohesive (∞,1)-topos

Structures with infinitesimal cohesion

infinitesimal cohesion?

Models

Discrete and concrete objects

Modalities, Closure and Reflection

Contents

Idea

An anti-reduced object or simple infinitesimal type is one whose reduction is the point, hence one consisting entirely of “infinitesimal extension”, i.e. an infinitesimally thickened point.

Definition

In the context of differential cohesion, an anti-reduced obect is an comodal type XX for the infinitesimal shape modality \Im

(X)*. \Im(X) \simeq \ast \,.

Examples

Formal moduli problems

In homotopy type theory/higher topos theory anti-reduced types are essentially what is also called “formal moduli problems” (these are typically required to satisfy one more condition besides being anti-reduced, namely being infinitesimally cohesive in the sense of Lurie).

cohesion

tangent cohesion

differential cohesion

graded differential cohesion

id id fermionic bosonic bosonic Rh rheonomic reduced infinitesimal infinitesimal & étale cohesive ʃ discrete discrete continuous * \array{ && id &\dashv& id \\ && \vee && \vee \\ &\stackrel{fermionic}{}& \rightrightarrows &\dashv& \rightsquigarrow & \stackrel{bosonic}{} \\ && \bot && \bot \\ &\stackrel{bosonic}{} & \rightsquigarrow &\dashv& \mathrm{R}\!\!\mathrm{h} & \stackrel{rheonomic}{} \\ && \vee && \vee \\ &\stackrel{reduced}{} & \Re &\dashv& \Im & \stackrel{infinitesimal}{} \\ && \bot && \bot \\ &\stackrel{infinitesimal}{}& \Im &\dashv& \& & \stackrel{\text{étale}}{} \\ && \vee && \vee \\ &\stackrel{cohesive}{}& ʃ &\dashv& \flat & \stackrel{discrete}{} \\ && \bot && \bot \\ &\stackrel{discrete}{}& \flat &\dashv& \sharp & \stackrel{continuous}{} \\ && \vee && \vee \\ && \emptyset &\dashv& \ast }

Last revised on March 5, 2015 at 17:47:46. See the history of this page for a list of all contributions to it.