- Snapshots of modern mathematics
- Pierre de Fermat and Andrew Wiles in Czech Republic stamps
- Stefan Banach (March 30, 1892 – August 8, 1945)
- Guessing the Numbers
- What is mathematics for Ehrhard Behrends
- What is mathematics for Krzysztof Ciesielski
- The Three Ducks Trick
- What is mathematics for Franka Brueckler

# From Henri Poincaré to Henri Paul de Saint-Gervais

Whether you are a student or a non-professional mathematician, you might know who Henri Poincaré is, or was, actually. What about Henri Paul de Saint-Gervais? Like Nicolas Bourbaki, Henri Paul de Saint-Gervais stands for a group of mathematicians. However the comparison between the two groups stops here, the latter being non-secret, and more focused.

Some experts may already know Henri Paul de Saint-Gervais as the authors of a book, published last year by the EMS.

This year they have released a wonderful website, **Analysis Situs**, through which they aim at sharing with a hopefully wider audience their fascination for Henri Poincaré and his heritage.

If not for youngsters, this multiple-entry site should definitely gain the interest of undergrads, more advanced students, and even professional mathematicians who want to get acquainted with or/and learn more about a whole field founded by Poincaré about a century ago, namely algebraic topology.

Even if you don’t speak French, you may enjoy some unique contents and in particular the numerous, highly professional videos made by Jos Leys, which will help you understand basic surfaces like Möbius strips, tori, Klein bottles, and more sophisticated objects as well. The concept of fundamental group, coined by Henri Poincaré in his 1895 paper *Analysis Situs*, will have no mystery for you afterwards. For instance, this video will help you understand what is sometimes called the `théorème du garçon de café‘ (or waiter’s theorem). And there are plenty of deeper results to learn from Henri Paul de Saint-Gervais.

**Sylvie Benzoni**

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