# Diffiety

Diffiety formalizes the concept of the solution space of a given system of PDEs.

You are welcome to the coming Summer XVII Diffiety School!

Please note that old diffiety site is available at diffiety.ac.ru. Very old diffiety school site (school.diffiety.org) is available here. More recent information about diffiety schools can be found here. For the latest school see “Most Recent School”

This site facilitates communication of Diffety research group. The aim is to discuss various Diffiety-related concepts in blogs and comments, develop lecture notes interactively and publish more robust material in pdf/tex form. For technical details see FAQ/HowTo section. The site is still under construction.

Diffiety formalizes the concept of the solution space of a given system of (non-linear) PDEs – much like an algebraic variety does with respect to solutions of a given system of algebraic equations.

For a good demo of site abilities please, see Presentation by Maria Sorokina. The thing is that the page text contains usual TeX formulas in dollars which are nicely rendered to the user. Comments may contain formulas as well, so it’s easy to discuss mathematics on this site.

UPDATE: Formulas are bad everywhere except above demo page because slashes were

## Preprints, etc

Here you may find our lecture notes, preprints and presentations.
Hamiltonian formalism on manifolds with singularities. (Maria Sorokina)

## Announcement of XIV Winter Diffiety School

Dear Colleagues,

We would like to announce “XIV Winter Diffiety School”. Please note that this year the School will consist of two parts.

First part will be held in Saint Petersburg hosted by Lyceum 239. Approximate dates are February 1 payday advance to February 6 of 2014. The program is mostly targeted at persons new to Diffiety. Besides that there will be separate lectures for veterans.

Second part will be held from March 2nd to March 12th of 2014 in Poland. The exact place will be finalized by January 10th, it depends on the number of participants.

This edition of the school will be held online payday loans in a workshop fashion and is aimed at the payday 2 wiki veterans of Diffiety. Please, let us know which topics you would like to discuss. Based on preferences of the audience various open problems will be presented as well as several mini-courses will be given to help to get on track with the problems.

We will appreciate if you could spread information about the school to all potentially interested students and postdoctoral researchers.

Hadamard’s lemma: Any smooth function $f$ in a starlike neighborhood of a point $z$ is representable in the form
$$f(x)=f(z) \sum_{i=1}^n (x_i-z_i)g_i(x), ;g_i\in {C^{\infty}(U)},$$
where $g_i$ are smooth functions.