Zehna, Peter W <br/><br/>
Elements of set theory 
Peter W. Zehna, Robert L. Johnson 
 - 2nd ed. 
 - Boston  Allyn and Bacon  1972 
 - ix, 197 p. ; 24 cm. 
<br/><br/>p. 179-180. 
<br/><br/><label>LCCN: </label>75-162879 
<br/><br/><label>Subjects--Topical Terms: </label><br/>Set theory<br/>Logic, Symbolic and mathematical