Walker, James A. <br/><br/>
Variation in linguistic systems / 
James A. Walker. 
 - 1st  ed. 
 - New York :  Routledge,  2010. 
 - xviii, 158  p. 
<br/><br/><label>ISBN: </label>0415990684 : 
<br/><br/><label>Subjects--Topical Terms: </label><br/>Language and languages--Variation.