From: carl_thinks_cs@yahoo.com   
      
   How does prolog use recursive descent parsing to solve problems given   
   to it?. Does it make a graph of the parse tree or something?   
      
   I've only encountered recursive descent parsing to solve problems like   
   boolean algebra or number arithmetic but prolog can do much more than   
   this.   
      
   I understand that it's easy enough to do for facts like.   
      
   male(bill).   
   female(mary).   
      
   one only has to compare the query to the facts in the database per   
   token. but what about rules like?   
      
   parent(X,Y):-mother(X,Y).   
   grandparent(X,Y):-parent(X,Z),parent(Z,Y).   
      
   I find it difficult to imagine that you would only check them per   
   token.   
      
   So, how does prolog handle this?   
      
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