
 Hausdorff, Felix  Hutchinson encyclopedia article about Hausdorff, Felix (Site not responding. Last check: 20071107) 
  Hausdorff was born in Breslau, Germany (now Wrocław, Poland), and studied at Berlin, Freiburg, and Leipzig. 
  Hausdorff formulated a theory of topological and metric spaces, proposing that such spaces be regarded as sets of points and sets of relations among the points, and introduced the principle of duality. 
  This principle states that an equation between sets remains valid if the sets are replaced by their complements and the symbol for union is exchanged for that of intersection. 
 encyclopedia.farlex.com /Hausdorff,+Felix (268 words) 
