The French sought an armistice with Germany which was concluded on 22 June. France was divided in two. German troops occupied the whole of northern France from the north coast to the Pyrenees. The rest of France nominally had full sovereignty, but the government set up at Vichy essentially cooperated with Germany. After British and American forces landed in North Africa in 1942, Germany occupied the whole of France. The Vichy government now directly implemented German policies.
François Le Lionnais was a French mathematician working in France during the period of the war. He planned a book Great Currents of Mathematical Thought during this period. The Foreword to the book was written by Jean Ballard, who was involved in the project, and his description of the period gives a remarkable insight into what it must have been like being a mathematician in France during the years of occupation:-
This work, the idea for which came to us during the occupation, has undergone many vicissitudes. Let me be permitted to recount them here as my sole excuse for appearing in such learned company.
François Le Lionnais was in Marseilles in 1942. Fascinated by the extent and, above all, the lucidity of his knowledge, I suggested that he solicit expository articles from the best mathematicians of the time and assemble these into a book which would present a picture of the ideas and spirit of present-day mathematics.
We agreed that this work should attempt to show not an immobile panorama of the different disciplines belonging to this science, but, above all, the different directions in which they were moving. We hoped that this would inaugurate a series of works on scientific humanism. We have kept the title chosen at that time because the word "currents" [courants] seemed to define correctly the perspective in which we viewed our efforts.
Neither of us had any doubts about the difficulties confronting such an enterprise in 1942, but we were far from imagining that five long years would be necessary to bring it into being. No one could foresee all the obstacles which would retard the execution of our plans. One need only recall the period when the Frenchmen of the two zones could only correspond by those postcards so strictly rationed by our prudential occupiers! No room was left for the imagination and still less for intellectual exchange. Into those parsimoniously counted lines we had to compress immense questions, suggest a complex design and outline problems which permitted no trifling with their statements.
There was no hope of finding contributors outside of France. The exiles were lost to us, ... . We were able to reach some of them since, but the same delays which allowed us to include André Weil, the brother of our sorely missed Simone Weil, caused us to lose the irreplaceable assistance of Paul Valéry, Leon Brunschvicg and Jean Cavaillès. During this period we had suffered the loss of two contributors who were unable to see the completion of the work, Albert Lautman, shot by the Germans at Toulouse, and Paul Mouy, whom we lost at the end of the year 1946.
Our work, despite so many obstacles and sorrows, went along slowly until a certain event stopped it cold. Le Lionnais, who belonged to a resistance group, was arrested at the end of April 1944 and taken to the concentration camp at Dora, where he was employed in the underground V2 factories during those endless months which were to pass until the advance of the Allies. Few enough returned from that notoriously dismal hell; our friend escaped the fate of the majority of the prisoners only because of his good health and high morale.
Among the hopes which sustained him, the project of the Main Currents of Mathematical Thought so occupied his mind that one day it almost cost him his fife. He had rewritten the summary from memory, when by an unfortunate accident he dropped in front of the guards a piece of wrapping paper on which certain names were written. He was called in to explain it to a police agent. The latter, as ignorant as only a prison guard can be, viewed everything in his own light. This man could see in the list of names Borel, Montel, de Broglie, Valéry, Brunschvicg, only a group of prisoners who wanted to give him the slip. It was impossible to make him change his mind; he demanded a complete confession: At what time, at what place were the accomplices to assemble? He finally let himself be convinced, but that did not prevent him from decreeing punishment for the crime of having written with a Nazi pencil on the paper of the Third Reich, and it was thus that for the love of mathematics our friend Le Lionnais received the mandatory lashes of the whip which might have killed him.
When he returned at the beginning of May 1945, long months were necessary in order for him to regain his health and readapt to normal life. His health had been greatly shaken and his papers had been destroyed, notably his article on beauty in mathematics. Thanks to the precautions he had taken, he was able to recover one by one copies of the texts already obtained; he sounded the rallying call again and the crew began anew to navigate toward their destination.
We cannot thank François Le Lionnais too much for his perseverance, praise him too much for his faith. In spite of many obstacles he has brought an important work into existence. All those who are devoted to works of the mind and especially to mathematical research will be grateful to him for having illuminated the problems which so arouse their interest with the best light the times can provide.
But let us take care not to forget the concern of the scholars who were not asked in vain, nor the collaboration of eminent minds, accorded with good will despite the many tasks which burdened them. We thank all the contributors to this work for their confidence and their devotion. We hope that they will find the justification of their efforts in the pleasure of seeing them assembled here.