Prawitz, Dag, <br/><br/>
Natural Deduction : 

 -  Courier Dover Publications,  2006. 
 - 132 pages 
<br/><br/><label>ISBN: </label>9780486446554 
<br/><br/><label>Subjects--Topical Terms: </label><br/>Mathematics.
<br/><br/><label>Dewey Class. No.: </label>162  / PRA