Cain, George L. <br/><br/>
Introduction to general topology 
George L. Cain 
 - Reading, Mass.  Addison-Wesley  1993 
 - 215 p. ; 24 cm. 
<br/><br/>p. 209. 
<br/><br/><label>ISBN: </label>0201576988 
<br/><br/><label>LCCN: </label>92-43576 
<br/><br/><label>Subjects--Topical Terms: </label><br/>Topology