title: How does the DPLL algorithm work?
body: <p>I'm having trouble understanding the DPLL algorithm for checking satisfiability of a sentence in propositional logic. 
  <a href="http://books.google.co.in/books?id=4fyShrIFXg4C&amp;pg=PA250&amp;lpg=PA250&amp;dq=DPLL+algorithm+from+artificial+intelligence+A+modern+approach&amp;source=bl&amp;ots=oOoZsT8KFd&amp;sig=pdmyUsQZZWw76guWY9eFJKyNsH0&amp;hl=en&amp;sa=X&amp;ei=vBFeUOf1EMLrrQeanoG4DQ&amp;ved=0CD0Q6AEwAw#v=onepage&amp;q&amp;f=false" rel="noreferrer">http://books.google.co.in/books?id=4fyShrIFXg4C&amp;pg=PA250&amp;lpg=PA250&amp;dq=DPLL+algorithm+from+artificial+intelligence+A+modern+approach&amp;source=bl&amp;ots=oOoZsT8KFd&amp;sig=pdmyUsQZZWw76guWY9eFJKyNsH0&amp;hl=en&amp;sa=X&amp;ei=vBFeUOf1EMLrrQeanoG4DQ&amp;ved=0CD0Q6AEwAw#v=onepage&amp;q&amp;f=false</a><br>
  <img src="https://i.stack.imgur.com/OzR6y.png" alt="enter image description here"></p>
  
  <p>This algorithm is taken from the book Artificial Intelligence A modern approach. I'm finding it really confusing with those many function recursions. In particular, what does the <code>EXTEND()</code> function do, and what's the purpose behind the recursive calls to <code>DPLL()</code> ?</p>