Description: Definition of a compact topology. A topology is compact iff any open
covering of its underlying set contains a finite subcovering
(Heine-Borel property). Definition C''' of BourbakiTop1 p. I.59.
Note: Bourbaki uses the term "quasi-compact" (saving "compact" for
"compact Hausdorff"), but it is not the modern usage (which we follow).
(Contributed by FL, 22-Dec-2008)