Amie Ferris-Rotman My father, Brian Rotman, who has died aged 87, was a mathematician, semiotician and occasional playwright. He helped shape how we think of mathematics as a cultural system, authoring seven books between 1966 and 2008. Signifying Nothing (1987) offered a fresh view of zero, showing how “nothing” reveals human knowledge structures, while Ad Infinitum … The Ghost in Turing's Machine (1993) argued that symbols and absences function more like ghosts than concrete entities.