APA
(1991). Compact unions of closed subsets are closed and compact intersections of open subsets are open. [s.l.]: [s.n.].
Chicago
1991. Compact unions of closed subsets are closed and compact intersections of open subsets are open. [s.l.]: [s.n.].
Harvard
(1991). Compact unions of closed subsets are closed and compact intersections of open subsets are open. [s.l.]: [s.n.].
MLA
Compact unions of closed subsets are closed and compact intersections of open subsets are open. [s.l.]: [s.n.]. 1991.