Like Descartes and Pascal, Hans Hahn (1879-1934) was both an eminent mathematician and a highly influential philosopher. He founded the Vienna Circle and was the teacher of both Kurt G del and Karl Popper. His seminal contributions to functional analysis and general topology had a huge impact on the development of modern analysis. Hahn's passionate interest in the foundations of mathematics, vividly described in Sir Karl Popper's foreword (which...