Hughes, G E  . <br/><br/>
An introduction to modal logic /  
G. E. Hughes and M. J. Cresswell. 
 - London :   Methuen ,   1968. 
 - xi, 388p. :   ills.,figs. ;   22cm  ` .  
<br/><br/>Includes index 
<br/><br/><label>ISBN: </label> NULL (Pb) 
<br/><br/><label>Subjects--Index Terms: </label>LOGIC 
<br/><br/><label>Dewey Class. No.: </label>160  / HUG/I