
 Gravity: Notation and Definitions 
  A topological space in which, for every pair of nonidentical points p and q, there exist two open sets P and Q containing them, that do not intersect (that is, whose intersection is empty). 
  It is a major theorem that every Hausdorff space is a metric space, that is, it has a distance function (and vice versa, an easy theorem). 
  A manifold is a Hausdorff space, with a countable basis of open sets, such that a neighborhood of every point (some open set containing the point) is homeomorphic to R 
 www.math.ucla.edu /~jimc/klein_h/notation.html (1120 words) 
