Blog on Leonid Ryvkin

Connections on anchored bundles

Mon, 07 Sep 2026 11:22:21 +0200

I was recently reading the very nice preprint arXiv:2608.07351, on how to construct a Lie algebroid over $\mathbb R^n$ whose underlying foliation is given by the vector fields vanishing up to a prescribed order $k$ and tried to translate the notion of left-symmetric algebroid used therein, in terms of connections. The following is a writeup of my thoughts.

Lectures in symplectic geometry, Fall 2026

Sat, 05 Sep 2026 00:00:00 +0000

This site contains the information on the master course on symplectic geometry that I teach in the Fall term 2026 in Lyon. Information about the master program can be found here.

If you want to receive emails concerning the lectures please register here.

Session log

Second session : 16. September, 9:45, building ‘Quai 43’, room 112 (first floor)

First session (09. September, 9:45):

In addition to the material in the lecture notes we have discussed what a category is, notes on this will be added to the lecture notes after lecture two.

Pen-and-Paper adventure

Tue, 24 Dec 2024 00:00:00 +0000

Josef Adamčík, Anna Marklová and I created an adventure for the Mausritter Pen-and-Paper role plaing game. It is called Chrismous Forever and can be downloaded here. The rules of the basic game are available here.

Scavenger Hunt

Tue, 21 Jun 2022 00:00:00 +0000

Alfonso Garmendia and I have created a scavenger hunt for the participants of the SFARS seminar, that we organized. It is still available here, the access code to start the hunt is “Request Mission”.

A few elementary riddles and excercises

Thu, 02 Dec 2021 00:00:00 +0000

I know some of the following from Benjamin Böhme, who in turn credits Wim Martens. If you know a source I should refer to for some of them, please let me know.

Subsets

Let $n\in \mathbb N$ be a natural number. Consider an $n+1$-element subset $A$ of $\{1,…,2n\}$. Show that $A$ contains two distinct numbers $a,b $, such that $a$ divides $b$.
Checkerboard

Consider a checkerboard of $n\times n$ fields. Some fields contain pieces, others don’t. Now put pieces on every field that touches (through its edges) at least two fields already containing pieces. Repeat the process until no further pieces are added. What is the minimal number of pieces on the field at the beginning of the procedure, if every field contains a piece at the end? (And why?)