# nLab formal smooth manifold

### Context

#### Synthetic differential geometry

differential geometry

synthetic differential geometry

# Contents

## Idea

A formal smooth manifold is a smooth manifold equipped possibly with infinitesimal extension.

In the differential cohesion of synthetic differential infinity-groupoids these are the spaces locally isomorphic to $\mathbb{R}^n \times D$, where $\mathbb{R}^n$ is a Cartesian space and $D$ is an infinitesimally thickened point. Here $\mathbb{R}^n$ is the underlying reduced manifold.

## References

Section I.17 and I.19 of

Formal smooth manifolds of the simple product form $X \times D$ in the category of smooth loci for $X$ an ordinary smooth manifold and $D$ and infinitesimal space have been considered in section 4 of

• Eduardo Dubuc, Sur les modeles de la geometrie differentielle synthetique Cahiers de Topologie et Géométrie Différentielle Catégoriques, 20 no. 3 (1979), p. 231-279 (numdam).

For more on this see Cahiers topos

Revised on June 3, 2014 07:21:26 by Urs Schreiber (89.204.155.45)