Mathematics in Difficult Times: The Hidden Collaboration of Elli and Heinrich Heesch
Have you ever heard of Elli Heesch (1904-1993), a German logician and philosopher who spent a brief research period at Princeton as a nun? You may have heard of her brother, Heinrich Heesch (1906–1995), a notable German mathematician recognised for developing the “discharging method”, which played a crucial role in the 1977 computer-aided proof of the four-colour theorem. However, the collaboration between Heinrich and Elli Heesch on tiling problems and their industrial applications during World War II remains largely unknown.