Karen Olsson:

In 1939, as the buildup to war in Europe intensified, a brilliant French mathematician named André Weil made a plan to emigrate to the U.S. He was thirty-three and didn’t want to serve in the army; his life’s purpose was math, he felt, not soldiering. His escape turned out to be more difficult than he anticipated, in part because, as he would write in his memoir, “the Americans, who so warmly welcome those who do not need them, are much less hospitable to those who happen to be at their mercy”—as we’ve gone on to prove repeatedly since then.

He was vacationing in Finland when the war broke out, and he tried to lay low in Helsinki but was arrested and returned to France, where he sat in jail during the spring of 1940, awaiting trial for desertion. While there, he took some consolation from the fact that jail allowed him to work undisturbed, as well as to read novels and write letters, in particular letters to his sister, Simone Weil, who was also remarkably talented, a philosopher and spiritual thinker.

Though her brother’s incarceration infuriated her, Simone saw an opportunity. His work in advanced mathematics was to her, as it would be to most of us, esoteric. Since you have some spare time on your hands, she wrote to him, why don’t you explain to me exactly what it is you do?