Хорошо известна история про то, что Лере придумал пучки и спектралки, сидя в концлагере. Чуть менее, но также известно, что он изначально занимался уравнениями в частных производных, а объявил себя топологом ради того, чтобы его не припахали работать в шаражке.
Оказывается, он устроил в концлагере целый университет, в частности, выдавший несколько сотен степеней, подтверждённых после войны:
https://en.wikipedia.org/wiki/Oflag_XVII-A#POW_activities
The prisoners were encouraged to occupy their time productively. They formed a choir and a theatre group, and built their own sports ground, the Stade Pétain. One of the most popular activities were the lectures at the Université en Captivité, headed by Lieutenant Jean Leray, formerly a mathematics professor at the Université de Nancy. The University awarded almost 500 degrees, all of which were officially confirmed after the war. Leray lectured mainly on calculus and topology, concealing his expertise in fluid dynamics and mechanics since he feared being forced to work on German military projects. He also studied algebraic topology, publishing several papers after the war on spectral sequences and sheaf theory. Other notable figures of the University were the embryologist Étienne Wolff and the geologist François Ellenberger. The syllabus also included such subjects as law, biology, psychology, Arabic, music, moral theology, and astronomy.[1]
The prisoners produced a weekly newspaper, Le Canard en KG. "KG" is the German abbreviation for Kriegsgefangener ("Prisoner of War"), and in French this was pronounced as Le canard encagé ("The Caged Duck"), a reference to the popular satirical journal Le Canard enchaîné.[1]
A more clandestine production was the 30-minute film[1] entitled Sous le Manteau ("Under The Cloak"), directed by Marcel Corre.[4] It was shot on 14 reels of 8 mm film on a camera hidden inside a hollowed-out dictionary, and recorded scenes of daily life in the camp, including prisoners at work on one of the 32 tunnels, totalling over 1 km (0.62 mi) in length, that were dug during the camp's lifetime.[5] According to Robert Christophe, Oflag XVII-A had a Gaullist resistance group called "La Maffia", which had ties to a French Resistance group (apparently the only such collaboration between prisoners outside France and resistance inside it), and thus acquired the materials for the camera as well as for escape attempts.[6]