Hughes G E <br/><br/>
Introduction to modal logic 
Hughes G E; Cresswell M J 
 - London  Methuen U. K.          1968 
 - xii, 388p  cm. 
<br/><br/> Bibliography: P 356-71 
<br/><br/><label>Source: </label> General Book 
<br/><br/><label>Subjects--Topical Terms: </label><br/>Philosophy-Logic
<br/><br/><label>Dewey Class. No.: </label>R1, K8