Hervé Lehning (1948–2022) | Tangente

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Passing on knowledge --------------------

It is impossible to speak of Hervé Lehning without mentioning his extraordinary career as a science communicator, just as it would be futile to try to compile an exhaustive list of the hundreds of articles he wrote for numerous scientific publications, most notably Tangente (he was, in particular, editor-in-chief of Tangente Sup). Hervé worked across every field and constantly sought to make everything accessible to the widest possible audience. Number theory, geometry, algebra, topology, analysis, computer science, philosophy and history, aesthetics, elections, modeling, statistics, cryptography: he explored all these worlds with skill, simplicity and rigor—a genuine tour de force. Fortunately, we still have his many books. One of the last of them encapsulates the full breadth of his talent and interests (it has even been translated into Chinese!) in its self-explanatory title: *Toutes les mathématiques du monde (All the Mathematics in the World)* (Flammarion, 2017).

A passion for cryptography --------------------------

Like most scientists, Hervé had "his" favorite fields. These also allowed him to bring his training as a historian—he held a master's degree in the history of religions—and his gifts as a storyteller to readers and audiences alike.

One of these fields was cryptography. In his *Bible des codes secrets (The Bible of Secret Codes) (Flammarion, 2019), he traces the evolution of this strange art of sophisticated concealment, from antiquity to the Internet and from Julius Caesar to today's computer systems, taking in the Enigma machine along the way. With passion and humor, he recounts a history that is (as he himself put it) "the history of the merciless struggle between those who have something to hide and those who would very much like to discover what is being hidden from them"*. Cryptography and military activities are difficult to separate. Hervé, the son of a serviceman, was also a reserve commander and a member of the Association des réservistes du chiffre et de la sécurité de l’information (ARCSI).

Photographer, artist and philosopher ------------------------------------

A captivating speaker, Hervé also liked to illustrate his talks with his own photographs. As he traveled through natural landscapes and cities around the world, he found remarkable illustrations of the properties, concepts and models of the mathematical world he sought to make more familiar and more vivid for us. But the beauty he saw in mathematics had also become a source of inspiration. He created a series of artworks and everyday objects (lamps and mugs), highlighting operations or equations in some cases and remarkable properties in others.

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From art to aesthetics and then philosophy, no field lay beyond our humanist. The latest post on his blog Math'monde (**blogs.futura-sciences.com/lehning**) was a response to a journalist who had recently claimed to "believe in science"; it explains why the statement is self-contradictory. For Hervé, science was a matter of facts.